Code Block with Syntax Highlighting (Prism-Style Token Colors)

Syntax highlighting is just CSS — the highlighter's only job is to wrap tokens in spans. This block hand-wraps a real ES2024 module in <span class="tok-keyword">, tok-string, tok-comment, tok-function, tok-variable, tok-number and tok-punct, then colours them from one oklch() token scale that follows the Prism / One Dark convention. Drop real Prism, Shiki or highlight.js output in later and the same rules light it up.

Live DemoAug 13, 2026

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The code

<div class="cbk-01">
  <button class="cbk-01__theme" type="button" aria-pressed="false" aria-label="Switch to dark theme">
    <svg class="cbk-01__moon" viewBox="0 0 24 24" aria-hidden="true" focusable="false"><path d="M20 14.2A8.2 8.2 0 0 1 9.8 4 8.4 8.4 0 1 0 20 14.2"/></svg>
    <svg class="cbk-01__sun" viewBox="0 0 24 24" aria-hidden="true" focusable="false"><circle cx="12" cy="12" r="4"/><path d="M12 3.4v2M12 18.6v2M3.4 12h2M18.6 12h2M6 6l1.4 1.4M16.6 16.6 18 18M18 6l-1.4 1.4M7.4 16.6 6 18"/></svg>
  </button>
  <div class="cbk-01__stage">
    <input class="cbk-01__tbox" id="cbk-01-tbox" type="checkbox" data-alt="light" aria-label="Toggle light and dark theme">
    <label class="cbk-01__tbtn" for="cbk-01-tbox" title="Toggle light and dark theme">
      <svg class="cbk-01__tsun" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.8" stroke-linecap="round" aria-hidden="true"><circle cx="12" cy="12" r="4.2"></circle><path d="M12 2.4v2.3M12 19.3v2.3M2.4 12h2.3M19.3 12h2.3M5.2 5.2l1.6 1.6M17.2 17.2l1.6 1.6M18.8 5.2l-1.6 1.6M6.8 17.2l-1.6 1.6"></path></svg>
      <svg class="cbk-01__tmoon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.8" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><path d="M20.2 14.6A8.6 8.6 0 0 1 9.4 3.8a8.6 8.6 0 1 0 10.8 10.8Z"></path></svg>
    </label>
    <figure class="cbk-01__block">
      <figcaption class="cbk-01__bar">
        <span class="cbk-01__dot" aria-hidden="true"></span>
        <span class="cbk-01__file">
          <svg viewBox="0 0 24 24" fill="none" aria-hidden="true" focusable="false"><path d="M6.5 3.5h7L18 8v12.5H6.5z" stroke="currentColor" stroke-width="1.5" stroke-linejoin="round"/><path d="M13 3.5V8h5" stroke="currentColor" stroke-width="1.5" stroke-linejoin="round"/></svg>
          loadWorkspaces.js
        </span>
        <span class="cbk-01__pill">Prism.js compatible</span>
        <span class="cbk-01__lang">JavaScript</span>
      </figcaption>
      <div class="cbk-01__scroll">
<pre class="cbk-01__pre"><code class="language-js"><span class="tok-comment">// Fetch a member's workspaces once, then serve from the LRU cache.</span>
<span class="tok-keyword">import</span> <span class="tok-punct">{</span> <span class="tok-variable">cache</span> <span class="tok-punct">}</span> <span class="tok-keyword">from</span> <span class="tok-string">'./lru-cache.mjs'</span><span class="tok-punct">;</span>

<span class="tok-keyword">const</span> <span class="tok-variable">ENDPOINT</span> <span class="tok-op">=</span> <span class="tok-string">'/api/v2/workspaces'</span><span class="tok-punct">;</span>
<span class="tok-keyword">const</span> <span class="tok-variable">TTL</span> <span class="tok-op">=</span> <span class="tok-number">60_000</span><span class="tok-punct">;</span>

<span class="tok-keyword">export</span> <span class="tok-keyword">async</span> <span class="tok-keyword">function</span> <span class="tok-function">loadWorkspaces</span><span class="tok-punct">(</span><span class="tok-variable">userId</span><span class="tok-punct">, {</span> <span class="tok-variable">limit</span> <span class="tok-op">=</span> <span class="tok-number">25</span> <span class="tok-punct">} = {}) {</span>
  <span class="tok-keyword">const</span> <span class="tok-variable">hit</span> <span class="tok-op">=</span> <span class="tok-variable">cache</span><span class="tok-punct">.</span><span class="tok-function">get</span><span class="tok-punct">(</span><span class="tok-variable">userId</span><span class="tok-punct">, </span><span class="tok-variable">TTL</span><span class="tok-punct">);</span>
  <span class="tok-keyword">if</span> <span class="tok-punct">(</span><span class="tok-variable">hit</span><span class="tok-punct">) </span><span class="tok-keyword">return</span> <span class="tok-variable">hit</span><span class="tok-punct">;</span>

  <span class="tok-keyword">const</span> <span class="tok-variable">res</span> <span class="tok-op">=</span> <span class="tok-keyword">await</span> <span class="tok-function">fetch</span><span class="tok-punct">(</span><span class="tok-string">`${ENDPOINT}?user=${userId}&amp;limit=${limit}`</span><span class="tok-punct">);</span>
  <span class="tok-keyword">if</span> <span class="tok-punct">(!</span><span class="tok-variable">res</span><span class="tok-punct">.</span><span class="tok-variable">ok</span><span class="tok-punct">) </span><span class="tok-keyword">throw</span> <span class="tok-keyword">new</span> <span class="tok-function">Error</span><span class="tok-punct">(</span><span class="tok-string">`workspaces ${res.status}`</span><span class="tok-punct">);</span>
  <span class="tok-keyword">return</span> <span class="tok-variable">cache</span><span class="tok-punct">.</span><span class="tok-function">set</span><span class="tok-punct">(</span><span class="tok-variable">userId</span><span class="tok-punct">, </span><span class="tok-keyword">await</span> <span class="tok-variable">res</span><span class="tok-punct">.</span><span class="tok-function">json</span><span class="tok-punct">());</span>
<span class="tok-punct">}</span></code></pre>
      </div>
    </figure>
  </div>
</div>

<div class="cbk-01">
  <button class="cbk-01__theme" type="button" aria-pressed="false" aria-label="Switch to dark theme">
    <svg class="cbk-01__moon" viewBox="0 0 24 24" aria-hidden="true" focusable="false"><path d="M20 14.2A8.2 8.2 0 0 1 9.8 4 8.4 8.4 0 1 0 20 14.2"/></svg>
    <svg class="cbk-01__sun" viewBox="0 0 24 24" aria-hidden="true" focusable="false"><circle cx="12" cy="12" r="4"/><path d="M12 3.4v2M12 18.6v2M3.4 12h2M18.6 12h2M6 6l1.4 1.4M16.6 16.6 18 18M18 6l-1.4 1.4M7.4 16.6 6 18"/></svg>
  </button>
  <div class="cbk-01__stage">
    <input class="cbk-01__tbox" id="cbk-01-tbox" type="checkbox" data-alt="light" aria-label="Toggle light and dark theme">
    <label class="cbk-01__tbtn" for="cbk-01-tbox" title="Toggle light and dark theme">
      <svg class="cbk-01__tsun" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.8" stroke-linecap="round" aria-hidden="true"><circle cx="12" cy="12" r="4.2"></circle><path d="M12 2.4v2.3M12 19.3v2.3M2.4 12h2.3M19.3 12h2.3M5.2 5.2l1.6 1.6M17.2 17.2l1.6 1.6M18.8 5.2l-1.6 1.6M6.8 17.2l-1.6 1.6"></path></svg>
      <svg class="cbk-01__tmoon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.8" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><path d="M20.2 14.6A8.6 8.6 0 0 1 9.4 3.8a8.6 8.6 0 1 0 10.8 10.8Z"></path></svg>
    </label>
    <figure class="cbk-01__block">
      <figcaption class="cbk-01__bar">
        <span class="cbk-01__dot" aria-hidden="true"></span>
        <span class="cbk-01__file">
          <svg viewBox="0 0 24 24" fill="none" aria-hidden="true" focusable="false"><path d="M6.5 3.5h7L18 8v12.5H6.5z" stroke="currentColor" stroke-width="1.5" stroke-linejoin="round"/><path d="M13 3.5V8h5" stroke="currentColor" stroke-width="1.5" stroke-linejoin="round"/></svg>
          loadWorkspaces.js
        </span>
        <span class="cbk-01__pill">Prism.js compatible</span>
        <span class="cbk-01__lang">JavaScript</span>
      </figcaption>
      <div class="cbk-01__scroll">
<pre class="cbk-01__pre"><code class="language-js"><span class="tok-comment">// Fetch a member's workspaces once, then serve from the LRU cache.</span>
<span class="tok-keyword">import</span> <span class="tok-punct">{</span> <span class="tok-variable">cache</span> <span class="tok-punct">}</span> <span class="tok-keyword">from</span> <span class="tok-string">'./lru-cache.mjs'</span><span class="tok-punct">;</span>

<span class="tok-keyword">const</span> <span class="tok-variable">ENDPOINT</span> <span class="tok-op">=</span> <span class="tok-string">'/api/v2/workspaces'</span><span class="tok-punct">;</span>
<span class="tok-keyword">const</span> <span class="tok-variable">TTL</span> <span class="tok-op">=</span> <span class="tok-number">60_000</span><span class="tok-punct">;</span>

<span class="tok-keyword">export</span> <span class="tok-keyword">async</span> <span class="tok-keyword">function</span> <span class="tok-function">loadWorkspaces</span><span class="tok-punct">(</span><span class="tok-variable">userId</span><span class="tok-punct">, {</span> <span class="tok-variable">limit</span> <span class="tok-op">=</span> <span class="tok-number">25</span> <span class="tok-punct">} = {}) {</span>
  <span class="tok-keyword">const</span> <span class="tok-variable">hit</span> <span class="tok-op">=</span> <span class="tok-variable">cache</span><span class="tok-punct">.</span><span class="tok-function">get</span><span class="tok-punct">(</span><span class="tok-variable">userId</span><span class="tok-punct">, </span><span class="tok-variable">TTL</span><span class="tok-punct">);</span>
  <span class="tok-keyword">if</span> <span class="tok-punct">(</span><span class="tok-variable">hit</span><span class="tok-punct">) </span><span class="tok-keyword">return</span> <span class="tok-variable">hit</span><span class="tok-punct">;</span>

  <span class="tok-keyword">const</span> <span class="tok-variable">res</span> <span class="tok-op">=</span> <span class="tok-keyword">await</span> <span class="tok-function">fetch</span><span class="tok-punct">(</span><span class="tok-string">`${ENDPOINT}?user=${userId}&amp;limit=${limit}`</span><span class="tok-punct">);</span>
  <span class="tok-keyword">if</span> <span class="tok-punct">(!</span><span class="tok-variable">res</span><span class="tok-punct">.</span><span class="tok-variable">ok</span><span class="tok-punct">) </span><span class="tok-keyword">throw</span> <span class="tok-keyword">new</span> <span class="tok-function">Error</span><span class="tok-punct">(</span><span class="tok-string">`workspaces ${res.status}`</span><span class="tok-punct">);</span>
  <span class="tok-keyword">return</span> <span class="tok-variable">cache</span><span class="tok-punct">.</span><span class="tok-function">set</span><span class="tok-punct">(</span><span class="tok-variable">userId</span><span class="tok-punct">, </span><span class="tok-keyword">await</span> <span class="tok-variable">res</span><span class="tok-punct">.</span><span class="tok-function">json</span><span class="tok-punct">());</span>
<span class="tok-punct">}</span></code></pre>
      </div>
    </figure>
  </div>
</div>

.cbk-01 {
  inline-size: 100%;
  width: 100%;
  min-block-size: 100vh;
  min-block-size: 100svh;
  min-height: 100vh;
  display: block;
  --mono: ui-monospace,"JetBrains Mono","Geist Mono","SF Mono","IBM Plex Mono",Menlo,monospace;
  --sans: system-ui,"Inter","Geist",-apple-system,"Segoe UI",sans-serif;
  --bg: #07080c;
  --surface: #0e1017;
  --bar: #12141d;
  --line: #232733;
  --ink: #e7eaf2;
  --muted: #98a0b0;
  --acc: #a78bfa;
  --tok-key: #d2a8ff;
  --tok-str: #7ee787;
  --tok-fn: #79c0ff;
  --tok-var: #ffcb6b;
  --tok-num: #ff85a1;
  --tok-com: #98a2b3;
  --tok-punct: #8b96a8;
  --tok-op: #ff9d6b;
  background: radial-gradient(60rem 34rem at 50% -10%, #171b2b 0%, transparent 62%) , var(--bg);
  color: var(--ink);
  font-family: var(--sans);
}

@supports (color: oklch(50% .1 200)) {
  .cbk-01 {
    --bg: oklch(13% .012 265);
    --surface: oklch(17% .015 265);
    --bar: oklch(20% .017 265);
    --line: oklch(28% .018 265);
    --ink: oklch(93% .008 265);
    --muted: oklch(70% .02 265);
    --acc: oklch(74% .16 300);
    --tok-key: oklch(80% .15 305);
    --tok-str: oklch(85% .18 148);
    --tok-fn: oklch(80% .13 245);
    --tok-var: oklch(85% .13 85);
    --tok-num: oklch(78% .15 5);
    --tok-com: oklch(72% .02 265);
    --tok-punct: oklch(68% .02 265);
    --tok-op: oklch(80% .13 45);
  }
}

.cbk-01 *,
.cbk-01 *::before,
.cbk-01 *::after {
  box-sizing: border-box;
}

.cbk-01__stage {
  display: grid;
  place-items: center;
  min-block-size: inherit;
  padding: clamp(1rem,4vw,3.5rem);
}

.cbk-01__block {
  margin: 0;
  inline-size: min(64rem,100%);
  border: 1px solid var(--line);
  border-radius: 16px;
  background: var(--surface);
  overflow: hidden;
  box-shadow: 0 1px 0 rgba(255,255,255,.05) inset, 0 24px 60px -28px rgba(0,0,0,.9);
}

.cbk-01__bar {
  display: flex;
  align-items: center;
  gap: .7rem;
  padding: .75rem 1rem;
  border-block-end: 1px solid var(--line);
  background: linear-gradient(180deg,var(--bar),var(--surface));
  font-size: .8125rem;
  flex-wrap: wrap;
}

.cbk-01__dot {
  inline-size: 9px;
  block-size: 9px;
  border-radius: 50%;
  background: var(--acc);
  box-shadow: 0 0 0 3px color-mix(in oklab,var(--acc) 22%,transparent);
}

.cbk-01__file {
  display: inline-flex;
  align-items: center;
  gap: .45rem;
  color: var(--ink);
  font-family: var(--mono);
  font-size: .8125rem;
}

.cbk-01__file svg {
  inline-size: 15px;
  block-size: 15px;
  color: var(--muted);
}

.cbk-01__pill {
  margin-inline-start: auto;
  padding: .2rem .55rem;
  border: 1px solid color-mix(in oklab,var(--acc) 38%,transparent);
  border-radius: 999px;
  background: color-mix(in oklab,var(--acc) 14%,transparent);
  color: var(--acc);
  font-size: .6875rem;
  font-weight: 600;
  letter-spacing: .06em;
  text-transform: uppercase;
}

.cbk-01__lang {
  padding: .2rem .5rem;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: var(--bg);
  color: var(--muted);
  font-family: var(--mono);
  font-size: .6875rem;
  letter-spacing: .04em;
}

.cbk-01__scroll {
  overflow: auto;
  scrollbar-gutter: stable;
  overscroll-behavior-inline: contain;
}

.cbk-01__pre {
  margin: 0;
  padding: 1.15rem 1.25rem 1.35rem;
  font-family: var(--mono);
  font-size: clamp(.8125rem,.42rem + .55cqi,.9375rem);
  line-height: 1.75;
  white-space: pre;
  tab-size: 2;
  font-variant-ligatures: none;
  color: var(--ink);
}

.cbk-01__pre code {
  font: inherit;
  color: inherit;
}

.cbk-01 .tok-keyword {
  color: var(--tok-key);
  font-weight: 500;
}

.cbk-01 .tok-string {
  color: var(--tok-str);
}

.cbk-01 .tok-function {
  color: var(--tok-fn);
}

.cbk-01 .tok-variable {
  color: var(--tok-var);
}

.cbk-01 .tok-number {
  color: var(--tok-num);
  font-variant-numeric: tabular-nums;
}

.cbk-01 .tok-comment {
  color: var(--tok-com);
  font-style: italic;
}

.cbk-01 .tok-punct {
  color: var(--tok-punct);
}

.cbk-01 .tok-op {
  color: var(--tok-op);
}

.cbk-01__scroll::-webkit-scrollbar {
  block-size: 10px;
}

.cbk-01__scroll::-webkit-scrollbar-thumb {
  background: var(--line);
  border-radius: 999px;
}

.cbk-01[data-theme="light"] {
  --bg: #f6f7fb;
  --surface: #ffffff;
  --bar: #f2f3f9;
  --line: #e3e6f0;
  --ink: #12141c;
  --muted: #5d6577;
  --acc: #7c3aed;
  --tok-key: #8250df;
  --tok-str: #0a7d3f;
  --tok-fn: #0550ae;
  --tok-var: #8a5a00;
  --tok-num: #b1265c;
  --tok-com: #5d6577;
  --tok-punct: #57606a;
  --tok-op: #a2410a;
  background: radial-gradient(60rem 34rem at 50% -10%, #e9ecff 0%, transparent 62%), var(--bg);
}

.cbk-01[data-theme="light"] .cbk-01__block {
  box-shadow: 0 1px 0 #fff inset, 0 18px 44px -30px rgba(16,20,40,.45);
}

@media (prefers-color-scheme: light) {
  .cbk-01:not([data-theme="dark"]) {
    --bg: #f6f7fb;
    --surface: #ffffff;
    --bar: #f2f3f9;
    --line: #e3e6f0;
    --ink: #12141c;
    --muted: #5d6577;
    --acc: #7c3aed;
    --tok-key: #8250df;
    --tok-str: #0a7d3f;
    --tok-fn: #0550ae;
    --tok-var: #8a5a00;
    --tok-num: #b1265c;
    --tok-com: #5d6577;
    --tok-punct: #57606a;
    --tok-op: #a2410a;
    background: radial-gradient(60rem 34rem at 50% -10%, #e9ecff 0%, transparent 62%), var(--bg);
  }

  .cbk-01:not([data-theme="dark"]) .cbk-01__block {
    box-shadow: 0 1px 0 #fff inset, 0 18px 44px -30px rgba(16,20,40,.45);
  }
}

@media (forced-colors: active) {
  .cbk-01__block {
    border: 2px solid CanvasText;
    background: Canvas;
  }

  .cbk-01__pill,
    .cbk-01__lang {
    border: 1px solid CanvasText;
    color: CanvasText;
    background: Canvas;
  }

  .cbk-01 [class^="tok-"] {
    color: CanvasText;
  }
}
/* theme toggle — pure CSS, :has() driven; :checked = light theme, top-right of the stage */

.cbk-01__stage {
  position: relative;
}

.cbk-01__tbox {
  position: absolute;
  inline-size: 1px;
  block-size: 1px;
  margin: 0;
  padding: 0;
  opacity: 0;
  pointer-events: none;
}

.cbk-01__tbtn {
  position: absolute;
  inset-block-start: clamp(.7rem,2vw,1.35rem);
  inset-inline-end: clamp(.7rem,2vw,1.35rem);
  z-index: 7;
  display: grid;
  place-items: center;
  inline-size: 2.375rem;
  block-size: 2.375rem;
  border: 1px solid rgba(127,127,127,.34);
  border-radius: 11px;
  background: rgba(127,127,127,.14);
  color: var(--ink,#e7eaf3);
  cursor: pointer;
  -webkit-backdrop-filter: blur(6px);
  backdrop-filter: blur(6px);
  transition: background .18s ease, border-color .18s ease, transform .18s ease;
}

@supports (color: color-mix(in srgb,red,blue)) {
  .cbk-01__tbtn {
    background: color-mix(in srgb, var(--ink,#e7eaf3) 10%, transparent);
    border-color: color-mix(in srgb, var(--ink,#e7eaf3) 26%, transparent);
  }
}

.cbk-01__tbtn:hover {
  transform: translateY(-1px);
}

.cbk-01__tbtn svg {
  inline-size: 1.0625rem;
  block-size: 1.0625rem;
}

.cbk-01__tbox:focus-visible + .cbk-01__tbtn {
  outline: 2px solid var(--ink,#e7eaf3);
  outline-offset: 2px;
}

.cbk-01__tmoon {
  display: none;
}

.cbk-01:has(.cbk-01__tbox:checked) .cbk-01__tsun {
  display: none;
}

.cbk-01:has(.cbk-01__tbox:checked) .cbk-01__tmoon {
  display: block;
}

@media (prefers-reduced-motion: reduce) {
  .cbk-01__tbtn {
    transition: none;
  }

  .cbk-01__tbtn:hover {
    transform: none;
  }
}

@media (forced-colors: active) {
  .cbk-01__tbtn {
    border: 1px solid ButtonBorder;
    color: ButtonText;
    background: ButtonFace;
  }
}

.cbk-01:has(.cbk-01__tbox:checked) {
  --bg: #f6f7fb;
  --surface: #ffffff;
  --bar: #f2f3f9;
  --line: #e3e6f0;
  --ink: #12141c;
  --muted: #5d6577;
  --acc: #7c3aed;
  --tok-key: #8250df;
  --tok-str: #0a7d3f;
  --tok-fn: #0550ae;
  --tok-var: #8a5a00;
  --tok-num: #b1265c;
  --tok-com: #5d6577;
  --tok-punct: #57606a;
  --tok-op: #a2410a;
  background: radial-gradient(60rem 34rem at 50% -10%, #e9ecff 0%, transparent 62%), var(--bg);
}

.cbk-01:has(.cbk-01__tbox:checked) .cbk-01__block {
  box-shadow: 0 1px 0 #fff inset, 0 18px 44px -30px rgba(16,20,40,.45);
}

.cbk-01__theme {
  position: absolute;
  inset-block-start: clamp(.75rem,2vw,1.25rem);
  inset-inline-end: clamp(.75rem,2vw,1.25rem);
  z-index: 50;
  inline-size: 2.5rem;
  block-size: 2.5rem;
  display: grid;
  place-items: center;
  cursor: pointer;
  padding: 0;
  border-radius: 999px;
  border: 1px solid rgba(0,0,0,.12);
  color: currentColor;
  background: rgba(255,255,255,.72);
  -webkit-backdrop-filter: blur(10px);
  backdrop-filter: blur(10px);
  transition: background .25s ease, transform .25s cubic-bezier(.16,1,.3,1), border-color .25s ease;
}

.cbk-01[data-theme="dark"] .cbk-01__theme {
  background: rgba(20,20,28,.72);
  border-color: rgba(255,255,255,.15);
  color: #fff;
}

@media (prefers-color-scheme: dark) {
  .cbk-01:not([data-theme="light"]) .cbk-01__theme {
    background: rgba(20,20,28,.72);
    border-color: rgba(255,255,255,.15);
    color: #fff;
  }
}

.cbk-01__theme:hover {
  transform: translateY(-1px);
  border-color: rgba(0,0,0,.24);
}

.cbk-01[data-theme="dark"] .cbk-01__theme:hover,
.cbk-01:not([data-theme="light"]) .cbk-01__theme:hover {
  border-color: rgba(255,255,255,.3);
}

.cbk-01__theme:focus-visible {
  outline: 2px solid currentColor;
  outline-offset: 3px;
}

.cbk-01__theme svg {
  grid-area: 1/1;
  inline-size: 1.1rem;
  block-size: 1.1rem;
  fill: none;
  stroke: currentColor;
  stroke-width: 1.7;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.cbk-01__sun {
  display: none;
}

.cbk-01__theme[aria-pressed="true"] .cbk-01__sun {
  display: block;
}

.cbk-01__theme[aria-pressed="true"] .cbk-01__moon {
  display: none;
}

@media (prefers-reduced-motion: reduce) {
  .cbk-01__theme {
    transition: none;
  }

  .cbk-01__theme:hover {
    transform: none;
  }
}

.cbk-01 {
  inline-size: 100%;
  width: 100%;
  min-block-size: 100vh;
  min-block-size: 100svh;
  min-height: 100vh;
  display: block;
  --mono: ui-monospace,"JetBrains Mono","Geist Mono","SF Mono","IBM Plex Mono",Menlo,monospace;
  --sans: system-ui,"Inter","Geist",-apple-system,"Segoe UI",sans-serif;
  --bg: #07080c;
  --surface: #0e1017;
  --bar: #12141d;
  --line: #232733;
  --ink: #e7eaf2;
  --muted: #98a0b0;
  --acc: #a78bfa;
  --tok-key: #d2a8ff;
  --tok-str: #7ee787;
  --tok-fn: #79c0ff;
  --tok-var: #ffcb6b;
  --tok-num: #ff85a1;
  --tok-com: #98a2b3;
  --tok-punct: #8b96a8;
  --tok-op: #ff9d6b;
  background: radial-gradient(60rem 34rem at 50% -10%, #171b2b 0%, transparent 62%) , var(--bg);
  color: var(--ink);
  font-family: var(--sans);
}

@supports (color: oklch(50% .1 200)) {
  .cbk-01 {
    --bg: oklch(13% .012 265);
    --surface: oklch(17% .015 265);
    --bar: oklch(20% .017 265);
    --line: oklch(28% .018 265);
    --ink: oklch(93% .008 265);
    --muted: oklch(70% .02 265);
    --acc: oklch(74% .16 300);
    --tok-key: oklch(80% .15 305);
    --tok-str: oklch(85% .18 148);
    --tok-fn: oklch(80% .13 245);
    --tok-var: oklch(85% .13 85);
    --tok-num: oklch(78% .15 5);
    --tok-com: oklch(72% .02 265);
    --tok-punct: oklch(68% .02 265);
    --tok-op: oklch(80% .13 45);
  }
}

.cbk-01 *,
.cbk-01 *::before,
.cbk-01 *::after {
  box-sizing: border-box;
}

.cbk-01__stage {
  display: grid;
  place-items: center;
  min-block-size: inherit;
  padding: clamp(1rem,4vw,3.5rem);
}

.cbk-01__block {
  margin: 0;
  inline-size: min(64rem,100%);
  border: 1px solid var(--line);
  border-radius: 16px;
  background: var(--surface);
  overflow: hidden;
  box-shadow: 0 1px 0 rgba(255,255,255,.05) inset, 0 24px 60px -28px rgba(0,0,0,.9);
}

.cbk-01__bar {
  display: flex;
  align-items: center;
  gap: .7rem;
  padding: .75rem 1rem;
  border-block-end: 1px solid var(--line);
  background: linear-gradient(180deg,var(--bar),var(--surface));
  font-size: .8125rem;
  flex-wrap: wrap;
}

.cbk-01__dot {
  inline-size: 9px;
  block-size: 9px;
  border-radius: 50%;
  background: var(--acc);
  box-shadow: 0 0 0 3px color-mix(in oklab,var(--acc) 22%,transparent);
}

.cbk-01__file {
  display: inline-flex;
  align-items: center;
  gap: .45rem;
  color: var(--ink);
  font-family: var(--mono);
  font-size: .8125rem;
}

.cbk-01__file svg {
  inline-size: 15px;
  block-size: 15px;
  color: var(--muted);
}

.cbk-01__pill {
  margin-inline-start: auto;
  padding: .2rem .55rem;
  border: 1px solid color-mix(in oklab,var(--acc) 38%,transparent);
  border-radius: 999px;
  background: color-mix(in oklab,var(--acc) 14%,transparent);
  color: var(--acc);
  font-size: .6875rem;
  font-weight: 600;
  letter-spacing: .06em;
  text-transform: uppercase;
}

.cbk-01__lang {
  padding: .2rem .5rem;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: var(--bg);
  color: var(--muted);
  font-family: var(--mono);
  font-size: .6875rem;
  letter-spacing: .04em;
}

.cbk-01__scroll {
  overflow: auto;
  scrollbar-gutter: stable;
  overscroll-behavior-inline: contain;
}

.cbk-01__pre {
  margin: 0;
  padding: 1.15rem 1.25rem 1.35rem;
  font-family: var(--mono);
  font-size: clamp(.8125rem,.42rem + .55cqi,.9375rem);
  line-height: 1.75;
  white-space: pre;
  tab-size: 2;
  font-variant-ligatures: none;
  color: var(--ink);
}

.cbk-01__pre code {
  font: inherit;
  color: inherit;
}

.cbk-01 .tok-keyword {
  color: var(--tok-key);
  font-weight: 500;
}

.cbk-01 .tok-string {
  color: var(--tok-str);
}

.cbk-01 .tok-function {
  color: var(--tok-fn);
}

.cbk-01 .tok-variable {
  color: var(--tok-var);
}

.cbk-01 .tok-number {
  color: var(--tok-num);
  font-variant-numeric: tabular-nums;
}

.cbk-01 .tok-comment {
  color: var(--tok-com);
  font-style: italic;
}

.cbk-01 .tok-punct {
  color: var(--tok-punct);
}

.cbk-01 .tok-op {
  color: var(--tok-op);
}

.cbk-01__scroll::-webkit-scrollbar {
  block-size: 10px;
}

.cbk-01__scroll::-webkit-scrollbar-thumb {
  background: var(--line);
  border-radius: 999px;
}

.cbk-01[data-theme="light"] {
  --bg: #f6f7fb;
  --surface: #ffffff;
  --bar: #f2f3f9;
  --line: #e3e6f0;
  --ink: #12141c;
  --muted: #5d6577;
  --acc: #7c3aed;
  --tok-key: #8250df;
  --tok-str: #0a7d3f;
  --tok-fn: #0550ae;
  --tok-var: #8a5a00;
  --tok-num: #b1265c;
  --tok-com: #5d6577;
  --tok-punct: #57606a;
  --tok-op: #a2410a;
  background: radial-gradient(60rem 34rem at 50% -10%, #e9ecff 0%, transparent 62%), var(--bg);
}

.cbk-01[data-theme="light"] .cbk-01__block {
  box-shadow: 0 1px 0 #fff inset, 0 18px 44px -30px rgba(16,20,40,.45);
}

@media (prefers-color-scheme: light) {
  .cbk-01:not([data-theme="dark"]) {
    --bg: #f6f7fb;
    --surface: #ffffff;
    --bar: #f2f3f9;
    --line: #e3e6f0;
    --ink: #12141c;
    --muted: #5d6577;
    --acc: #7c3aed;
    --tok-key: #8250df;
    --tok-str: #0a7d3f;
    --tok-fn: #0550ae;
    --tok-var: #8a5a00;
    --tok-num: #b1265c;
    --tok-com: #5d6577;
    --tok-punct: #57606a;
    --tok-op: #a2410a;
    background: radial-gradient(60rem 34rem at 50% -10%, #e9ecff 0%, transparent 62%), var(--bg);
  }

  .cbk-01:not([data-theme="dark"]) .cbk-01__block {
    box-shadow: 0 1px 0 #fff inset, 0 18px 44px -30px rgba(16,20,40,.45);
  }
}

@media (forced-colors: active) {
  .cbk-01__block {
    border: 2px solid CanvasText;
    background: Canvas;
  }

  .cbk-01__pill,
    .cbk-01__lang {
    border: 1px solid CanvasText;
    color: CanvasText;
    background: Canvas;
  }

  .cbk-01 [class^="tok-"] {
    color: CanvasText;
  }
}
/* theme toggle — pure CSS, :has() driven; :checked = light theme, top-right of the stage */

.cbk-01__stage {
  position: relative;
}

.cbk-01__tbox {
  position: absolute;
  inline-size: 1px;
  block-size: 1px;
  margin: 0;
  padding: 0;
  opacity: 0;
  pointer-events: none;
}

.cbk-01__tbtn {
  position: absolute;
  inset-block-start: clamp(.7rem,2vw,1.35rem);
  inset-inline-end: clamp(.7rem,2vw,1.35rem);
  z-index: 7;
  display: grid;
  place-items: center;
  inline-size: 2.375rem;
  block-size: 2.375rem;
  border: 1px solid rgba(127,127,127,.34);
  border-radius: 11px;
  background: rgba(127,127,127,.14);
  color: var(--ink,#e7eaf3);
  cursor: pointer;
  -webkit-backdrop-filter: blur(6px);
  backdrop-filter: blur(6px);
  transition: background .18s ease, border-color .18s ease, transform .18s ease;
}

@supports (color: color-mix(in srgb,red,blue)) {
  .cbk-01__tbtn {
    background: color-mix(in srgb, var(--ink,#e7eaf3) 10%, transparent);
    border-color: color-mix(in srgb, var(--ink,#e7eaf3) 26%, transparent);
  }
}

.cbk-01__tbtn:hover {
  transform: translateY(-1px);
}

.cbk-01__tbtn svg {
  inline-size: 1.0625rem;
  block-size: 1.0625rem;
}

.cbk-01__tbox:focus-visible + .cbk-01__tbtn {
  outline: 2px solid var(--ink,#e7eaf3);
  outline-offset: 2px;
}

.cbk-01__tmoon {
  display: none;
}

.cbk-01:has(.cbk-01__tbox:checked) .cbk-01__tsun {
  display: none;
}

.cbk-01:has(.cbk-01__tbox:checked) .cbk-01__tmoon {
  display: block;
}

@media (prefers-reduced-motion: reduce) {
  .cbk-01__tbtn {
    transition: none;
  }

  .cbk-01__tbtn:hover {
    transform: none;
  }
}

@media (forced-colors: active) {
  .cbk-01__tbtn {
    border: 1px solid ButtonBorder;
    color: ButtonText;
    background: ButtonFace;
  }
}

.cbk-01:has(.cbk-01__tbox:checked) {
  --bg: #f6f7fb;
  --surface: #ffffff;
  --bar: #f2f3f9;
  --line: #e3e6f0;
  --ink: #12141c;
  --muted: #5d6577;
  --acc: #7c3aed;
  --tok-key: #8250df;
  --tok-str: #0a7d3f;
  --tok-fn: #0550ae;
  --tok-var: #8a5a00;
  --tok-num: #b1265c;
  --tok-com: #5d6577;
  --tok-punct: #57606a;
  --tok-op: #a2410a;
  background: radial-gradient(60rem 34rem at 50% -10%, #e9ecff 0%, transparent 62%), var(--bg);
}

.cbk-01:has(.cbk-01__tbox:checked) .cbk-01__block {
  box-shadow: 0 1px 0 #fff inset, 0 18px 44px -30px rgba(16,20,40,.45);
}

.cbk-01__theme {
  position: absolute;
  inset-block-start: clamp(.75rem,2vw,1.25rem);
  inset-inline-end: clamp(.75rem,2vw,1.25rem);
  z-index: 50;
  inline-size: 2.5rem;
  block-size: 2.5rem;
  display: grid;
  place-items: center;
  cursor: pointer;
  padding: 0;
  border-radius: 999px;
  border: 1px solid rgba(0,0,0,.12);
  color: currentColor;
  background: rgba(255,255,255,.72);
  -webkit-backdrop-filter: blur(10px);
  backdrop-filter: blur(10px);
  transition: background .25s ease, transform .25s cubic-bezier(.16,1,.3,1), border-color .25s ease;
}

.cbk-01[data-theme="dark"] .cbk-01__theme {
  background: rgba(20,20,28,.72);
  border-color: rgba(255,255,255,.15);
  color: #fff;
}

@media (prefers-color-scheme: dark) {
  .cbk-01:not([data-theme="light"]) .cbk-01__theme {
    background: rgba(20,20,28,.72);
    border-color: rgba(255,255,255,.15);
    color: #fff;
  }
}

.cbk-01__theme:hover {
  transform: translateY(-1px);
  border-color: rgba(0,0,0,.24);
}

.cbk-01[data-theme="dark"] .cbk-01__theme:hover,
.cbk-01:not([data-theme="light"]) .cbk-01__theme:hover {
  border-color: rgba(255,255,255,.3);
}

.cbk-01__theme:focus-visible {
  outline: 2px solid currentColor;
  outline-offset: 3px;
}

.cbk-01__theme svg {
  grid-area: 1/1;
  inline-size: 1.1rem;
  block-size: 1.1rem;
  fill: none;
  stroke: currentColor;
  stroke-width: 1.7;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.cbk-01__sun {
  display: none;
}

.cbk-01__theme[aria-pressed="true"] .cbk-01__sun {
  display: block;
}

.cbk-01__theme[aria-pressed="true"] .cbk-01__moon {
  display: none;
}

@media (prefers-reduced-motion: reduce) {
  .cbk-01__theme {
    transition: none;
  }

  .cbk-01__theme:hover {
    transform: none;
  }
}

(()=>{const r=document.querySelector('.cbk-01');if(!r)return;const t=r.querySelector('.cbk-01__theme');if(!t)return;const dark=()=>(r.dataset.theme||(matchMedia('(prefers-color-scheme: dark)').matches?'dark':'light'))==='dark';const sync=()=>{t.setAttribute('aria-pressed',String(dark()));t.setAttribute('aria-label',dark()?'Switch to light theme':'Switch to dark theme');};t.addEventListener('click',()=>{r.dataset.theme=dark()?'light':'dark';sync();});matchMedia('(prefers-color-scheme: dark)').addEventListener('change',()=>{if(!r.dataset.theme)sync();});sync();})();

(()=>{const r=document.querySelector('.cbk-01');if(!r)return;const t=r.querySelector('.cbk-01__theme');if(!t)return;const dark=()=>(r.dataset.theme||(matchMedia('(prefers-color-scheme: dark)').matches?'dark':'light'))==='dark';const sync=()=>{t.setAttribute('aria-pressed',String(dark()));t.setAttribute('aria-label',dark()?'Switch to light theme':'Switch to dark theme');};t.addEventListener('click',()=>{r.dataset.theme=dark()?'light':'dark';sync();});matchMedia('(prefers-color-scheme: dark)').addEventListener('change',()=>{if(!r.dataset.theme)sync();});sync();})();

Here's a working CSS Code Block from CodeFronts. Use it as-is or adapt to your framework. All classes are scoped under a unique prefix so the code won't collide with your existing styles. MIT licensed.
Demo: Code Block with Syntax Highlighting (Prism-Style Token Colors)
Source: https://codefronts.com/snippets/css-code-blocks/code-block-with-syntax-highlighting-prism-style-token-colors/

Syntax highlighting is just CSS — the highlighter's only job is to wrap tokens in spans. This block hand-wraps a real ES2024 module in <span class="tok-keyword">, tok-string, tok-comment, tok-function, tok-variable, tok-number and tok-punct, then colours them from one oklch() token scale that follows the Prism / One Dark convention. Drop real Prism, Shiki or highlight.js output in later and the same rules light it up.
## HTML
```html
<div class="cbk-01">
  <button class="cbk-01__theme" type="button" aria-pressed="false" aria-label="Switch to dark theme">
    <svg class="cbk-01__moon" viewBox="0 0 24 24" aria-hidden="true" focusable="false"><path d="M20 14.2A8.2 8.2 0 0 1 9.8 4 8.4 8.4 0 1 0 20 14.2"/></svg>
    <svg class="cbk-01__sun" viewBox="0 0 24 24" aria-hidden="true" focusable="false"><circle cx="12" cy="12" r="4"/><path d="M12 3.4v2M12 18.6v2M3.4 12h2M18.6 12h2M6 6l1.4 1.4M16.6 16.6 18 18M18 6l-1.4 1.4M7.4 16.6 6 18"/></svg>
  </button>
  <div class="cbk-01__stage">
    <input class="cbk-01__tbox" id="cbk-01-tbox" type="checkbox" data-alt="light" aria-label="Toggle light and dark theme">
    <label class="cbk-01__tbtn" for="cbk-01-tbox" title="Toggle light and dark theme">
      <svg class="cbk-01__tsun" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.8" stroke-linecap="round" aria-hidden="true"><circle cx="12" cy="12" r="4.2"></circle><path d="M12 2.4v2.3M12 19.3v2.3M2.4 12h2.3M19.3 12h2.3M5.2 5.2l1.6 1.6M17.2 17.2l1.6 1.6M18.8 5.2l-1.6 1.6M6.8 17.2l-1.6 1.6"></path></svg>
      <svg class="cbk-01__tmoon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.8" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><path d="M20.2 14.6A8.6 8.6 0 0 1 9.4 3.8a8.6 8.6 0 1 0 10.8 10.8Z"></path></svg>
    </label>
    <figure class="cbk-01__block">
      <figcaption class="cbk-01__bar">
        <span class="cbk-01__dot" aria-hidden="true"></span>
        <span class="cbk-01__file">
          <svg viewBox="0 0 24 24" fill="none" aria-hidden="true" focusable="false"><path d="M6.5 3.5h7L18 8v12.5H6.5z" stroke="currentColor" stroke-width="1.5" stroke-linejoin="round"/><path d="M13 3.5V8h5" stroke="currentColor" stroke-width="1.5" stroke-linejoin="round"/></svg>
          loadWorkspaces.js
        </span>
        <span class="cbk-01__pill">Prism.js compatible</span>
        <span class="cbk-01__lang">JavaScript</span>
      </figcaption>
      <div class="cbk-01__scroll">
<pre class="cbk-01__pre"><code class="language-js"><span class="tok-comment">// Fetch a member's workspaces once, then serve from the LRU cache.</span>
<span class="tok-keyword">import</span> <span class="tok-punct">{</span> <span class="tok-variable">cache</span> <span class="tok-punct">}</span> <span class="tok-keyword">from</span> <span class="tok-string">'./lru-cache.mjs'</span><span class="tok-punct">;</span>

<span class="tok-keyword">const</span> <span class="tok-variable">ENDPOINT</span> <span class="tok-op">=</span> <span class="tok-string">'/api/v2/workspaces'</span><span class="tok-punct">;</span>
<span class="tok-keyword">const</span> <span class="tok-variable">TTL</span> <span class="tok-op">=</span> <span class="tok-number">60_000</span><span class="tok-punct">;</span>

<span class="tok-keyword">export</span> <span class="tok-keyword">async</span> <span class="tok-keyword">function</span> <span class="tok-function">loadWorkspaces</span><span class="tok-punct">(</span><span class="tok-variable">userId</span><span class="tok-punct">, {</span> <span class="tok-variable">limit</span> <span class="tok-op">=</span> <span class="tok-number">25</span> <span class="tok-punct">} = {}) {</span>
  <span class="tok-keyword">const</span> <span class="tok-variable">hit</span> <span class="tok-op">=</span> <span class="tok-variable">cache</span><span class="tok-punct">.</span><span class="tok-function">get</span><span class="tok-punct">(</span><span class="tok-variable">userId</span><span class="tok-punct">, </span><span class="tok-variable">TTL</span><span class="tok-punct">);</span>
  <span class="tok-keyword">if</span> <span class="tok-punct">(</span><span class="tok-variable">hit</span><span class="tok-punct">) </span><span class="tok-keyword">return</span> <span class="tok-variable">hit</span><span class="tok-punct">;</span>

  <span class="tok-keyword">const</span> <span class="tok-variable">res</span> <span class="tok-op">=</span> <span class="tok-keyword">await</span> <span class="tok-function">fetch</span><span class="tok-punct">(</span><span class="tok-string">`${ENDPOINT}?user=${userId}&amp;limit=${limit}`</span><span class="tok-punct">);</span>
  <span class="tok-keyword">if</span> <span class="tok-punct">(!</span><span class="tok-variable">res</span><span class="tok-punct">.</span><span class="tok-variable">ok</span><span class="tok-punct">) </span><span class="tok-keyword">throw</span> <span class="tok-keyword">new</span> <span class="tok-function">Error</span><span class="tok-punct">(</span><span class="tok-string">`workspaces ${res.status}`</span><span class="tok-punct">);</span>
  <span class="tok-keyword">return</span> <span class="tok-variable">cache</span><span class="tok-punct">.</span><span class="tok-function">set</span><span class="tok-punct">(</span><span class="tok-variable">userId</span><span class="tok-punct">, </span><span class="tok-keyword">await</span> <span class="tok-variable">res</span><span class="tok-punct">.</span><span class="tok-function">json</span><span class="tok-punct">());</span>
<span class="tok-punct">}</span></code></pre>
      </div>
    </figure>
  </div>
</div>
```
## CSS
```css
.cbk-01 {
  inline-size: 100%;
  width: 100%;
  min-block-size: 100vh;
  min-block-size: 100svh;
  min-height: 100vh;
  display: block;
  --mono: ui-monospace,"JetBrains Mono","Geist Mono","SF Mono","IBM Plex Mono",Menlo,monospace;
  --sans: system-ui,"Inter","Geist",-apple-system,"Segoe UI",sans-serif;
  --bg: #07080c;
  --surface: #0e1017;
  --bar: #12141d;
  --line: #232733;
  --ink: #e7eaf2;
  --muted: #98a0b0;
  --acc: #a78bfa;
  --tok-key: #d2a8ff;
  --tok-str: #7ee787;
  --tok-fn: #79c0ff;
  --tok-var: #ffcb6b;
  --tok-num: #ff85a1;
  --tok-com: #98a2b3;
  --tok-punct: #8b96a8;
  --tok-op: #ff9d6b;
  background: radial-gradient(60rem 34rem at 50% -10%, #171b2b 0%, transparent 62%) , var(--bg);
  color: var(--ink);
  font-family: var(--sans);
}

@supports (color: oklch(50% .1 200)) {
  .cbk-01 {
    --bg: oklch(13% .012 265);
    --surface: oklch(17% .015 265);
    --bar: oklch(20% .017 265);
    --line: oklch(28% .018 265);
    --ink: oklch(93% .008 265);
    --muted: oklch(70% .02 265);
    --acc: oklch(74% .16 300);
    --tok-key: oklch(80% .15 305);
    --tok-str: oklch(85% .18 148);
    --tok-fn: oklch(80% .13 245);
    --tok-var: oklch(85% .13 85);
    --tok-num: oklch(78% .15 5);
    --tok-com: oklch(72% .02 265);
    --tok-punct: oklch(68% .02 265);
    --tok-op: oklch(80% .13 45);
  }
}

.cbk-01 *,
.cbk-01 *::before,
.cbk-01 *::after {
  box-sizing: border-box;
}

.cbk-01__stage {
  display: grid;
  place-items: center;
  min-block-size: inherit;
  padding: clamp(1rem,4vw,3.5rem);
}

.cbk-01__block {
  margin: 0;
  inline-size: min(64rem,100%);
  border: 1px solid var(--line);
  border-radius: 16px;
  background: var(--surface);
  overflow: hidden;
  box-shadow: 0 1px 0 rgba(255,255,255,.05) inset, 0 24px 60px -28px rgba(0,0,0,.9);
}

.cbk-01__bar {
  display: flex;
  align-items: center;
  gap: .7rem;
  padding: .75rem 1rem;
  border-block-end: 1px solid var(--line);
  background: linear-gradient(180deg,var(--bar),var(--surface));
  font-size: .8125rem;
  flex-wrap: wrap;
}

.cbk-01__dot {
  inline-size: 9px;
  block-size: 9px;
  border-radius: 50%;
  background: var(--acc);
  box-shadow: 0 0 0 3px color-mix(in oklab,var(--acc) 22%,transparent);
}

.cbk-01__file {
  display: inline-flex;
  align-items: center;
  gap: .45rem;
  color: var(--ink);
  font-family: var(--mono);
  font-size: .8125rem;
}

.cbk-01__file svg {
  inline-size: 15px;
  block-size: 15px;
  color: var(--muted);
}

.cbk-01__pill {
  margin-inline-start: auto;
  padding: .2rem .55rem;
  border: 1px solid color-mix(in oklab,var(--acc) 38%,transparent);
  border-radius: 999px;
  background: color-mix(in oklab,var(--acc) 14%,transparent);
  color: var(--acc);
  font-size: .6875rem;
  font-weight: 600;
  letter-spacing: .06em;
  text-transform: uppercase;
}

.cbk-01__lang {
  padding: .2rem .5rem;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: var(--bg);
  color: var(--muted);
  font-family: var(--mono);
  font-size: .6875rem;
  letter-spacing: .04em;
}

.cbk-01__scroll {
  overflow: auto;
  scrollbar-gutter: stable;
  overscroll-behavior-inline: contain;
}

.cbk-01__pre {
  margin: 0;
  padding: 1.15rem 1.25rem 1.35rem;
  font-family: var(--mono);
  font-size: clamp(.8125rem,.42rem + .55cqi,.9375rem);
  line-height: 1.75;
  white-space: pre;
  tab-size: 2;
  font-variant-ligatures: none;
  color: var(--ink);
}

.cbk-01__pre code {
  font: inherit;
  color: inherit;
}

.cbk-01 .tok-keyword {
  color: var(--tok-key);
  font-weight: 500;
}

.cbk-01 .tok-string {
  color: var(--tok-str);
}

.cbk-01 .tok-function {
  color: var(--tok-fn);
}

.cbk-01 .tok-variable {
  color: var(--tok-var);
}

.cbk-01 .tok-number {
  color: var(--tok-num);
  font-variant-numeric: tabular-nums;
}

.cbk-01 .tok-comment {
  color: var(--tok-com);
  font-style: italic;
}

.cbk-01 .tok-punct {
  color: var(--tok-punct);
}

.cbk-01 .tok-op {
  color: var(--tok-op);
}

.cbk-01__scroll::-webkit-scrollbar {
  block-size: 10px;
}

.cbk-01__scroll::-webkit-scrollbar-thumb {
  background: var(--line);
  border-radius: 999px;
}

.cbk-01[data-theme="light"] {
  --bg: #f6f7fb;
  --surface: #ffffff;
  --bar: #f2f3f9;
  --line: #e3e6f0;
  --ink: #12141c;
  --muted: #5d6577;
  --acc: #7c3aed;
  --tok-key: #8250df;
  --tok-str: #0a7d3f;
  --tok-fn: #0550ae;
  --tok-var: #8a5a00;
  --tok-num: #b1265c;
  --tok-com: #5d6577;
  --tok-punct: #57606a;
  --tok-op: #a2410a;
  background: radial-gradient(60rem 34rem at 50% -10%, #e9ecff 0%, transparent 62%), var(--bg);
}

.cbk-01[data-theme="light"] .cbk-01__block {
  box-shadow: 0 1px 0 #fff inset, 0 18px 44px -30px rgba(16,20,40,.45);
}

@media (prefers-color-scheme: light) {
  .cbk-01:not([data-theme="dark"]) {
    --bg: #f6f7fb;
    --surface: #ffffff;
    --bar: #f2f3f9;
    --line: #e3e6f0;
    --ink: #12141c;
    --muted: #5d6577;
    --acc: #7c3aed;
    --tok-key: #8250df;
    --tok-str: #0a7d3f;
    --tok-fn: #0550ae;
    --tok-var: #8a5a00;
    --tok-num: #b1265c;
    --tok-com: #5d6577;
    --tok-punct: #57606a;
    --tok-op: #a2410a;
    background: radial-gradient(60rem 34rem at 50% -10%, #e9ecff 0%, transparent 62%), var(--bg);
  }

  .cbk-01:not([data-theme="dark"]) .cbk-01__block {
    box-shadow: 0 1px 0 #fff inset, 0 18px 44px -30px rgba(16,20,40,.45);
  }
}

@media (forced-colors: active) {
  .cbk-01__block {
    border: 2px solid CanvasText;
    background: Canvas;
  }

  .cbk-01__pill,
    .cbk-01__lang {
    border: 1px solid CanvasText;
    color: CanvasText;
    background: Canvas;
  }

  .cbk-01 [class^="tok-"] {
    color: CanvasText;
  }
}
/* theme toggle — pure CSS, :has() driven; :checked = light theme, top-right of the stage */

.cbk-01__stage {
  position: relative;
}

.cbk-01__tbox {
  position: absolute;
  inline-size: 1px;
  block-size: 1px;
  margin: 0;
  padding: 0;
  opacity: 0;
  pointer-events: none;
}

.cbk-01__tbtn {
  position: absolute;
  inset-block-start: clamp(.7rem,2vw,1.35rem);
  inset-inline-end: clamp(.7rem,2vw,1.35rem);
  z-index: 7;
  display: grid;
  place-items: center;
  inline-size: 2.375rem;
  block-size: 2.375rem;
  border: 1px solid rgba(127,127,127,.34);
  border-radius: 11px;
  background: rgba(127,127,127,.14);
  color: var(--ink,#e7eaf3);
  cursor: pointer;
  -webkit-backdrop-filter: blur(6px);
  backdrop-filter: blur(6px);
  transition: background .18s ease, border-color .18s ease, transform .18s ease;
}

@supports (color: color-mix(in srgb,red,blue)) {
  .cbk-01__tbtn {
    background: color-mix(in srgb, var(--ink,#e7eaf3) 10%, transparent);
    border-color: color-mix(in srgb, var(--ink,#e7eaf3) 26%, transparent);
  }
}

.cbk-01__tbtn:hover {
  transform: translateY(-1px);
}

.cbk-01__tbtn svg {
  inline-size: 1.0625rem;
  block-size: 1.0625rem;
}

.cbk-01__tbox:focus-visible + .cbk-01__tbtn {
  outline: 2px solid var(--ink,#e7eaf3);
  outline-offset: 2px;
}

.cbk-01__tmoon {
  display: none;
}

.cbk-01:has(.cbk-01__tbox:checked) .cbk-01__tsun {
  display: none;
}

.cbk-01:has(.cbk-01__tbox:checked) .cbk-01__tmoon {
  display: block;
}

@media (prefers-reduced-motion: reduce) {
  .cbk-01__tbtn {
    transition: none;
  }

  .cbk-01__tbtn:hover {
    transform: none;
  }
}

@media (forced-colors: active) {
  .cbk-01__tbtn {
    border: 1px solid ButtonBorder;
    color: ButtonText;
    background: ButtonFace;
  }
}

.cbk-01:has(.cbk-01__tbox:checked) {
  --bg: #f6f7fb;
  --surface: #ffffff;
  --bar: #f2f3f9;
  --line: #e3e6f0;
  --ink: #12141c;
  --muted: #5d6577;
  --acc: #7c3aed;
  --tok-key: #8250df;
  --tok-str: #0a7d3f;
  --tok-fn: #0550ae;
  --tok-var: #8a5a00;
  --tok-num: #b1265c;
  --tok-com: #5d6577;
  --tok-punct: #57606a;
  --tok-op: #a2410a;
  background: radial-gradient(60rem 34rem at 50% -10%, #e9ecff 0%, transparent 62%), var(--bg);
}

.cbk-01:has(.cbk-01__tbox:checked) .cbk-01__block {
  box-shadow: 0 1px 0 #fff inset, 0 18px 44px -30px rgba(16,20,40,.45);
}

.cbk-01__theme {
  position: absolute;
  inset-block-start: clamp(.75rem,2vw,1.25rem);
  inset-inline-end: clamp(.75rem,2vw,1.25rem);
  z-index: 50;
  inline-size: 2.5rem;
  block-size: 2.5rem;
  display: grid;
  place-items: center;
  cursor: pointer;
  padding: 0;
  border-radius: 999px;
  border: 1px solid rgba(0,0,0,.12);
  color: currentColor;
  background: rgba(255,255,255,.72);
  -webkit-backdrop-filter: blur(10px);
  backdrop-filter: blur(10px);
  transition: background .25s ease, transform .25s cubic-bezier(.16,1,.3,1), border-color .25s ease;
}

.cbk-01[data-theme="dark"] .cbk-01__theme {
  background: rgba(20,20,28,.72);
  border-color: rgba(255,255,255,.15);
  color: #fff;
}

@media (prefers-color-scheme: dark) {
  .cbk-01:not([data-theme="light"]) .cbk-01__theme {
    background: rgba(20,20,28,.72);
    border-color: rgba(255,255,255,.15);
    color: #fff;
  }
}

.cbk-01__theme:hover {
  transform: translateY(-1px);
  border-color: rgba(0,0,0,.24);
}

.cbk-01[data-theme="dark"] .cbk-01__theme:hover,
.cbk-01:not([data-theme="light"]) .cbk-01__theme:hover {
  border-color: rgba(255,255,255,.3);
}

.cbk-01__theme:focus-visible {
  outline: 2px solid currentColor;
  outline-offset: 3px;
}

.cbk-01__theme svg {
  grid-area: 1/1;
  inline-size: 1.1rem;
  block-size: 1.1rem;
  fill: none;
  stroke: currentColor;
  stroke-width: 1.7;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.cbk-01__sun {
  display: none;
}

.cbk-01__theme[aria-pressed="true"] .cbk-01__sun {
  display: block;
}

.cbk-01__theme[aria-pressed="true"] .cbk-01__moon {
  display: none;
}

@media (prefers-reduced-motion: reduce) {
  .cbk-01__theme {
    transition: none;
  }

  .cbk-01__theme:hover {
    transform: none;
  }
}
```

## JavaScript
```js
(()=>{const r=document.querySelector('.cbk-01');if(!r)return;const t=r.querySelector('.cbk-01__theme');if(!t)return;const dark=()=>(r.dataset.theme||(matchMedia('(prefers-color-scheme: dark)').matches?'dark':'light'))==='dark';const sync=()=>{t.setAttribute('aria-pressed',String(dark()));t.setAttribute('aria-label',dark()?'Switch to light theme':'Switch to dark theme');};t.addEventListener('click',()=>{r.dataset.theme=dark()?'light':'dark';sync();});matchMedia('(prefers-color-scheme: dark)').addEventListener('change',()=>{if(!r.dataset.theme)sync();});sync();})();
```

Paste this into ChatGPT, Claude, Cursor, or any coding assistant. The block below is pre-framed with everything the AI needs to integrate this demo into your project — markup, styles, scoping notes, and the source URL. Hit Copy and paste straight into your chat.

Here's a working CSS Code Block from CodeFronts. Use it as-is or adapt to your framework. All classes are scoped under a unique prefix so the code won't collide with your existing styles. MIT licensed.
Demo: Code Block with Syntax Highlighting (Prism-Style Token Colors)
Source: https://codefronts.com/snippets/css-code-blocks/code-block-with-syntax-highlighting-prism-style-token-colors/

Syntax highlighting is just CSS — the highlighter's only job is to wrap tokens in spans. This block hand-wraps a real ES2024 module in <span class="tok-keyword">, tok-string, tok-comment, tok-function, tok-variable, tok-number and tok-punct, then colours them from one oklch() token scale that follows the Prism / One Dark convention. Drop real Prism, Shiki or highlight.js output in later and the same rules light it up.
## HTML
```html
<div class="cbk-01">
  <button class="cbk-01__theme" type="button" aria-pressed="false" aria-label="Switch to dark theme">
    <svg class="cbk-01__moon" viewBox="0 0 24 24" aria-hidden="true" focusable="false"><path d="M20 14.2A8.2 8.2 0 0 1 9.8 4 8.4 8.4 0 1 0 20 14.2"/></svg>
    <svg class="cbk-01__sun" viewBox="0 0 24 24" aria-hidden="true" focusable="false"><circle cx="12" cy="12" r="4"/><path d="M12 3.4v2M12 18.6v2M3.4 12h2M18.6 12h2M6 6l1.4 1.4M16.6 16.6 18 18M18 6l-1.4 1.4M7.4 16.6 6 18"/></svg>
  </button>
  <div class="cbk-01__stage">
    <input class="cbk-01__tbox" id="cbk-01-tbox" type="checkbox" data-alt="light" aria-label="Toggle light and dark theme">
    <label class="cbk-01__tbtn" for="cbk-01-tbox" title="Toggle light and dark theme">
      <svg class="cbk-01__tsun" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.8" stroke-linecap="round" aria-hidden="true"><circle cx="12" cy="12" r="4.2"></circle><path d="M12 2.4v2.3M12 19.3v2.3M2.4 12h2.3M19.3 12h2.3M5.2 5.2l1.6 1.6M17.2 17.2l1.6 1.6M18.8 5.2l-1.6 1.6M6.8 17.2l-1.6 1.6"></path></svg>
      <svg class="cbk-01__tmoon" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.8" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><path d="M20.2 14.6A8.6 8.6 0 0 1 9.4 3.8a8.6 8.6 0 1 0 10.8 10.8Z"></path></svg>
    </label>
    <figure class="cbk-01__block">
      <figcaption class="cbk-01__bar">
        <span class="cbk-01__dot" aria-hidden="true"></span>
        <span class="cbk-01__file">
          <svg viewBox="0 0 24 24" fill="none" aria-hidden="true" focusable="false"><path d="M6.5 3.5h7L18 8v12.5H6.5z" stroke="currentColor" stroke-width="1.5" stroke-linejoin="round"/><path d="M13 3.5V8h5" stroke="currentColor" stroke-width="1.5" stroke-linejoin="round"/></svg>
          loadWorkspaces.js
        </span>
        <span class="cbk-01__pill">Prism.js compatible</span>
        <span class="cbk-01__lang">JavaScript</span>
      </figcaption>
      <div class="cbk-01__scroll">
<pre class="cbk-01__pre"><code class="language-js"><span class="tok-comment">// Fetch a member's workspaces once, then serve from the LRU cache.</span>
<span class="tok-keyword">import</span> <span class="tok-punct">{</span> <span class="tok-variable">cache</span> <span class="tok-punct">}</span> <span class="tok-keyword">from</span> <span class="tok-string">'./lru-cache.mjs'</span><span class="tok-punct">;</span>

<span class="tok-keyword">const</span> <span class="tok-variable">ENDPOINT</span> <span class="tok-op">=</span> <span class="tok-string">'/api/v2/workspaces'</span><span class="tok-punct">;</span>
<span class="tok-keyword">const</span> <span class="tok-variable">TTL</span> <span class="tok-op">=</span> <span class="tok-number">60_000</span><span class="tok-punct">;</span>

<span class="tok-keyword">export</span> <span class="tok-keyword">async</span> <span class="tok-keyword">function</span> <span class="tok-function">loadWorkspaces</span><span class="tok-punct">(</span><span class="tok-variable">userId</span><span class="tok-punct">, {</span> <span class="tok-variable">limit</span> <span class="tok-op">=</span> <span class="tok-number">25</span> <span class="tok-punct">} = {}) {</span>
  <span class="tok-keyword">const</span> <span class="tok-variable">hit</span> <span class="tok-op">=</span> <span class="tok-variable">cache</span><span class="tok-punct">.</span><span class="tok-function">get</span><span class="tok-punct">(</span><span class="tok-variable">userId</span><span class="tok-punct">, </span><span class="tok-variable">TTL</span><span class="tok-punct">);</span>
  <span class="tok-keyword">if</span> <span class="tok-punct">(</span><span class="tok-variable">hit</span><span class="tok-punct">) </span><span class="tok-keyword">return</span> <span class="tok-variable">hit</span><span class="tok-punct">;</span>

  <span class="tok-keyword">const</span> <span class="tok-variable">res</span> <span class="tok-op">=</span> <span class="tok-keyword">await</span> <span class="tok-function">fetch</span><span class="tok-punct">(</span><span class="tok-string">`${ENDPOINT}?user=${userId}&amp;limit=${limit}`</span><span class="tok-punct">);</span>
  <span class="tok-keyword">if</span> <span class="tok-punct">(!</span><span class="tok-variable">res</span><span class="tok-punct">.</span><span class="tok-variable">ok</span><span class="tok-punct">) </span><span class="tok-keyword">throw</span> <span class="tok-keyword">new</span> <span class="tok-function">Error</span><span class="tok-punct">(</span><span class="tok-string">`workspaces ${res.status}`</span><span class="tok-punct">);</span>
  <span class="tok-keyword">return</span> <span class="tok-variable">cache</span><span class="tok-punct">.</span><span class="tok-function">set</span><span class="tok-punct">(</span><span class="tok-variable">userId</span><span class="tok-punct">, </span><span class="tok-keyword">await</span> <span class="tok-variable">res</span><span class="tok-punct">.</span><span class="tok-function">json</span><span class="tok-punct">());</span>
<span class="tok-punct">}</span></code></pre>
      </div>
    </figure>
  </div>
</div>
```
## CSS
```css
.cbk-01 {
  inline-size: 100%;
  width: 100%;
  min-block-size: 100vh;
  min-block-size: 100svh;
  min-height: 100vh;
  display: block;
  --mono: ui-monospace,"JetBrains Mono","Geist Mono","SF Mono","IBM Plex Mono",Menlo,monospace;
  --sans: system-ui,"Inter","Geist",-apple-system,"Segoe UI",sans-serif;
  --bg: #07080c;
  --surface: #0e1017;
  --bar: #12141d;
  --line: #232733;
  --ink: #e7eaf2;
  --muted: #98a0b0;
  --acc: #a78bfa;
  --tok-key: #d2a8ff;
  --tok-str: #7ee787;
  --tok-fn: #79c0ff;
  --tok-var: #ffcb6b;
  --tok-num: #ff85a1;
  --tok-com: #98a2b3;
  --tok-punct: #8b96a8;
  --tok-op: #ff9d6b;
  background: radial-gradient(60rem 34rem at 50% -10%, #171b2b 0%, transparent 62%) , var(--bg);
  color: var(--ink);
  font-family: var(--sans);
}

@supports (color: oklch(50% .1 200)) {
  .cbk-01 {
    --bg: oklch(13% .012 265);
    --surface: oklch(17% .015 265);
    --bar: oklch(20% .017 265);
    --line: oklch(28% .018 265);
    --ink: oklch(93% .008 265);
    --muted: oklch(70% .02 265);
    --acc: oklch(74% .16 300);
    --tok-key: oklch(80% .15 305);
    --tok-str: oklch(85% .18 148);
    --tok-fn: oklch(80% .13 245);
    --tok-var: oklch(85% .13 85);
    --tok-num: oklch(78% .15 5);
    --tok-com: oklch(72% .02 265);
    --tok-punct: oklch(68% .02 265);
    --tok-op: oklch(80% .13 45);
  }
}

.cbk-01 *,
.cbk-01 *::before,
.cbk-01 *::after {
  box-sizing: border-box;
}

.cbk-01__stage {
  display: grid;
  place-items: center;
  min-block-size: inherit;
  padding: clamp(1rem,4vw,3.5rem);
}

.cbk-01__block {
  margin: 0;
  inline-size: min(64rem,100%);
  border: 1px solid var(--line);
  border-radius: 16px;
  background: var(--surface);
  overflow: hidden;
  box-shadow: 0 1px 0 rgba(255,255,255,.05) inset, 0 24px 60px -28px rgba(0,0,0,.9);
}

.cbk-01__bar {
  display: flex;
  align-items: center;
  gap: .7rem;
  padding: .75rem 1rem;
  border-block-end: 1px solid var(--line);
  background: linear-gradient(180deg,var(--bar),var(--surface));
  font-size: .8125rem;
  flex-wrap: wrap;
}

.cbk-01__dot {
  inline-size: 9px;
  block-size: 9px;
  border-radius: 50%;
  background: var(--acc);
  box-shadow: 0 0 0 3px color-mix(in oklab,var(--acc) 22%,transparent);
}

.cbk-01__file {
  display: inline-flex;
  align-items: center;
  gap: .45rem;
  color: var(--ink);
  font-family: var(--mono);
  font-size: .8125rem;
}

.cbk-01__file svg {
  inline-size: 15px;
  block-size: 15px;
  color: var(--muted);
}

.cbk-01__pill {
  margin-inline-start: auto;
  padding: .2rem .55rem;
  border: 1px solid color-mix(in oklab,var(--acc) 38%,transparent);
  border-radius: 999px;
  background: color-mix(in oklab,var(--acc) 14%,transparent);
  color: var(--acc);
  font-size: .6875rem;
  font-weight: 600;
  letter-spacing: .06em;
  text-transform: uppercase;
}

.cbk-01__lang {
  padding: .2rem .5rem;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: var(--bg);
  color: var(--muted);
  font-family: var(--mono);
  font-size: .6875rem;
  letter-spacing: .04em;
}

.cbk-01__scroll {
  overflow: auto;
  scrollbar-gutter: stable;
  overscroll-behavior-inline: contain;
}

.cbk-01__pre {
  margin: 0;
  padding: 1.15rem 1.25rem 1.35rem;
  font-family: var(--mono);
  font-size: clamp(.8125rem,.42rem + .55cqi,.9375rem);
  line-height: 1.75;
  white-space: pre;
  tab-size: 2;
  font-variant-ligatures: none;
  color: var(--ink);
}

.cbk-01__pre code {
  font: inherit;
  color: inherit;
}

.cbk-01 .tok-keyword {
  color: var(--tok-key);
  font-weight: 500;
}

.cbk-01 .tok-string {
  color: var(--tok-str);
}

.cbk-01 .tok-function {
  color: var(--tok-fn);
}

.cbk-01 .tok-variable {
  color: var(--tok-var);
}

.cbk-01 .tok-number {
  color: var(--tok-num);
  font-variant-numeric: tabular-nums;
}

.cbk-01 .tok-comment {
  color: var(--tok-com);
  font-style: italic;
}

.cbk-01 .tok-punct {
  color: var(--tok-punct);
}

.cbk-01 .tok-op {
  color: var(--tok-op);
}

.cbk-01__scroll::-webkit-scrollbar {
  block-size: 10px;
}

.cbk-01__scroll::-webkit-scrollbar-thumb {
  background: var(--line);
  border-radius: 999px;
}

.cbk-01[data-theme="light"] {
  --bg: #f6f7fb;
  --surface: #ffffff;
  --bar: #f2f3f9;
  --line: #e3e6f0;
  --ink: #12141c;
  --muted: #5d6577;
  --acc: #7c3aed;
  --tok-key: #8250df;
  --tok-str: #0a7d3f;
  --tok-fn: #0550ae;
  --tok-var: #8a5a00;
  --tok-num: #b1265c;
  --tok-com: #5d6577;
  --tok-punct: #57606a;
  --tok-op: #a2410a;
  background: radial-gradient(60rem 34rem at 50% -10%, #e9ecff 0%, transparent 62%), var(--bg);
}

.cbk-01[data-theme="light"] .cbk-01__block {
  box-shadow: 0 1px 0 #fff inset, 0 18px 44px -30px rgba(16,20,40,.45);
}

@media (prefers-color-scheme: light) {
  .cbk-01:not([data-theme="dark"]) {
    --bg: #f6f7fb;
    --surface: #ffffff;
    --bar: #f2f3f9;
    --line: #e3e6f0;
    --ink: #12141c;
    --muted: #5d6577;
    --acc: #7c3aed;
    --tok-key: #8250df;
    --tok-str: #0a7d3f;
    --tok-fn: #0550ae;
    --tok-var: #8a5a00;
    --tok-num: #b1265c;
    --tok-com: #5d6577;
    --tok-punct: #57606a;
    --tok-op: #a2410a;
    background: radial-gradient(60rem 34rem at 50% -10%, #e9ecff 0%, transparent 62%), var(--bg);
  }

  .cbk-01:not([data-theme="dark"]) .cbk-01__block {
    box-shadow: 0 1px 0 #fff inset, 0 18px 44px -30px rgba(16,20,40,.45);
  }
}

@media (forced-colors: active) {
  .cbk-01__block {
    border: 2px solid CanvasText;
    background: Canvas;
  }

  .cbk-01__pill,
    .cbk-01__lang {
    border: 1px solid CanvasText;
    color: CanvasText;
    background: Canvas;
  }

  .cbk-01 [class^="tok-"] {
    color: CanvasText;
  }
}
/* theme toggle — pure CSS, :has() driven; :checked = light theme, top-right of the stage */

.cbk-01__stage {
  position: relative;
}

.cbk-01__tbox {
  position: absolute;
  inline-size: 1px;
  block-size: 1px;
  margin: 0;
  padding: 0;
  opacity: 0;
  pointer-events: none;
}

.cbk-01__tbtn {
  position: absolute;
  inset-block-start: clamp(.7rem,2vw,1.35rem);
  inset-inline-end: clamp(.7rem,2vw,1.35rem);
  z-index: 7;
  display: grid;
  place-items: center;
  inline-size: 2.375rem;
  block-size: 2.375rem;
  border: 1px solid rgba(127,127,127,.34);
  border-radius: 11px;
  background: rgba(127,127,127,.14);
  color: var(--ink,#e7eaf3);
  cursor: pointer;
  -webkit-backdrop-filter: blur(6px);
  backdrop-filter: blur(6px);
  transition: background .18s ease, border-color .18s ease, transform .18s ease;
}

@supports (color: color-mix(in srgb,red,blue)) {
  .cbk-01__tbtn {
    background: color-mix(in srgb, var(--ink,#e7eaf3) 10%, transparent);
    border-color: color-mix(in srgb, var(--ink,#e7eaf3) 26%, transparent);
  }
}

.cbk-01__tbtn:hover {
  transform: translateY(-1px);
}

.cbk-01__tbtn svg {
  inline-size: 1.0625rem;
  block-size: 1.0625rem;
}

.cbk-01__tbox:focus-visible + .cbk-01__tbtn {
  outline: 2px solid var(--ink,#e7eaf3);
  outline-offset: 2px;
}

.cbk-01__tmoon {
  display: none;
}

.cbk-01:has(.cbk-01__tbox:checked) .cbk-01__tsun {
  display: none;
}

.cbk-01:has(.cbk-01__tbox:checked) .cbk-01__tmoon {
  display: block;
}

@media (prefers-reduced-motion: reduce) {
  .cbk-01__tbtn {
    transition: none;
  }

  .cbk-01__tbtn:hover {
    transform: none;
  }
}

@media (forced-colors: active) {
  .cbk-01__tbtn {
    border: 1px solid ButtonBorder;
    color: ButtonText;
    background: ButtonFace;
  }
}

.cbk-01:has(.cbk-01__tbox:checked) {
  --bg: #f6f7fb;
  --surface: #ffffff;
  --bar: #f2f3f9;
  --line: #e3e6f0;
  --ink: #12141c;
  --muted: #5d6577;
  --acc: #7c3aed;
  --tok-key: #8250df;
  --tok-str: #0a7d3f;
  --tok-fn: #0550ae;
  --tok-var: #8a5a00;
  --tok-num: #b1265c;
  --tok-com: #5d6577;
  --tok-punct: #57606a;
  --tok-op: #a2410a;
  background: radial-gradient(60rem 34rem at 50% -10%, #e9ecff 0%, transparent 62%), var(--bg);
}

.cbk-01:has(.cbk-01__tbox:checked) .cbk-01__block {
  box-shadow: 0 1px 0 #fff inset, 0 18px 44px -30px rgba(16,20,40,.45);
}

.cbk-01__theme {
  position: absolute;
  inset-block-start: clamp(.75rem,2vw,1.25rem);
  inset-inline-end: clamp(.75rem,2vw,1.25rem);
  z-index: 50;
  inline-size: 2.5rem;
  block-size: 2.5rem;
  display: grid;
  place-items: center;
  cursor: pointer;
  padding: 0;
  border-radius: 999px;
  border: 1px solid rgba(0,0,0,.12);
  color: currentColor;
  background: rgba(255,255,255,.72);
  -webkit-backdrop-filter: blur(10px);
  backdrop-filter: blur(10px);
  transition: background .25s ease, transform .25s cubic-bezier(.16,1,.3,1), border-color .25s ease;
}

.cbk-01[data-theme="dark"] .cbk-01__theme {
  background: rgba(20,20,28,.72);
  border-color: rgba(255,255,255,.15);
  color: #fff;
}

@media (prefers-color-scheme: dark) {
  .cbk-01:not([data-theme="light"]) .cbk-01__theme {
    background: rgba(20,20,28,.72);
    border-color: rgba(255,255,255,.15);
    color: #fff;
  }
}

.cbk-01__theme:hover {
  transform: translateY(-1px);
  border-color: rgba(0,0,0,.24);
}

.cbk-01[data-theme="dark"] .cbk-01__theme:hover,
.cbk-01:not([data-theme="light"]) .cbk-01__theme:hover {
  border-color: rgba(255,255,255,.3);
}

.cbk-01__theme:focus-visible {
  outline: 2px solid currentColor;
  outline-offset: 3px;
}

.cbk-01__theme svg {
  grid-area: 1/1;
  inline-size: 1.1rem;
  block-size: 1.1rem;
  fill: none;
  stroke: currentColor;
  stroke-width: 1.7;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.cbk-01__sun {
  display: none;
}

.cbk-01__theme[aria-pressed="true"] .cbk-01__sun {
  display: block;
}

.cbk-01__theme[aria-pressed="true"] .cbk-01__moon {
  display: none;
}

@media (prefers-reduced-motion: reduce) {
  .cbk-01__theme {
    transition: none;
  }

  .cbk-01__theme:hover {
    transform: none;
  }
}
```

## JavaScript
```js
(()=>{const r=document.querySelector('.cbk-01');if(!r)return;const t=r.querySelector('.cbk-01__theme');if(!t)return;const dark=()=>(r.dataset.theme||(matchMedia('(prefers-color-scheme: dark)').matches?'dark':'light'))==='dark';const sync=()=>{t.setAttribute('aria-pressed',String(dark()));t.setAttribute('aria-label',dark()?'Switch to light theme':'Switch to dark theme');};t.addEventListener('click',()=>{r.dataset.theme=dark()?'light':'dark';sync();});matchMedia('(prefers-color-scheme: dark)').addEventListener('change',()=>{if(!r.dataset.theme)sync();});sync();})();
```

How this works

1 — the only markup rule that matters. A highlighter is a tokenizer plus a class name. Prism emits <span class="token keyword">, Shiki emits inline styles, highlight.js emits hljs-keyword. Pick your class convention, wrap once, and colour in CSS:

<pre><code class="language-js"><span class="tok-keyword">export</span> <span class="tok-keyword">async</span> <span class="tok-keyword">function</span> <span class="tok-function">loadWorkspaces</span>(…)</code></pre>

2 — one scale, seven roles. Every colour is a custom property on the root, so re-theming the whole block (or matching your brand) is seven declarations, not a stylesheet crawl:

.cbk-01{
  --tok-key:#d2a8ff;  /* keyword   violet */
  --tok-str:#7ee787;  /* string    green  */
  --tok-fn:#79c0ff;   /* function  blue   */
  --tok-var:#ffcb6b;  /* variable  amber  */
  --tok-num:#ff7b9c;  /* number    pink   */
  --tok-com:#8b949e;  /* comment   grey   */
}
@supports (color: oklch(0 0 0)){
  .cbk-01{ --tok-key:oklch(78% .16 305); --tok-str:oklch(85% .19 145); }
}

3 — why oklch matters here. Six hues picked in hex drift wildly in perceived lightness, so one token screams and another disappears. In oklch() you hold the first number steady (all of these sit at 78-86% L) and only move hue, which is why this palette reads as one family and every token clears 4.5:1 against the surface.

4 — comments are the accessibility trap. The classic grey comment lands around 3:1. This demo lifts comments to a 4.6:1 grey and marks them italic as well, so the distinction survives greyscale, low vision and forced-colors mode — colour is never the only signal.

Make it yours

Retheme in seven lines: change --tok-key, --tok-str, --tok-fn, --tok-var, --tok-num, --tok-com, --tok-punct. Keep the lightness in the 78-86% band and only rotate hue.
Switch to real Prism markup by aliasing its classes once: .token.keyword{color:var(--tok-key)} .token.string{color:var(--tok-str)} — the rest of the block is untouched.
Add a language: nothing to install. New token roles (JSX tags, CSS at-rules, JSON keys) are just extra classes on the same scale.
Make it light-first by moving the [data-theme="light"] token block onto the root and swapping the media query.
Change the font by editing --mono; the stack already falls back through JetBrains Mono, Geist Mono and SF Mono to ui-monospace.
Add line numbers by combining with demo 12 — the token spans and the counter gutter are independent layers.

Gotchas — read before shipping

Never let a highlighter's white-space reset reach <pre>. Keep white-space: pre (this demo) or pre-wrap; normal collapses your indentation permanently.
Do not use text-wrap: pretty or balance on code — they are paragraph algorithms and will rag your lines in ways that change how the snippet reads. Chrome ignores them under white-space: pre, but other engines may not.
Escape < and & in code content. A raw <div> inside <code> becomes a real element and vanishes; < is not optional.
Ligature fonts turn =>, !== and <= into single glyphs that confuse learners copying character by character. font-variant-ligatures: none is deliberate.
Do not colour by opacity (color: rgb(255 255 255 / .5)). It fails contrast at small sizes and breaks completely on non-flat backgrounds; use a solid derived colour.
In forced-colors: active all token colours are overridden by the OS palette. That is correct behaviour — this is why comments also carry italics.
tab-size only affects real tab characters. If your snippet is space-indented (most are) it does nothing — normalise indentation at build time instead.

Browser support

Chrome	Safari	Firefox	Edge
111+	16.4+	113+	111+

The demo itself works everywhere — token colouring is plain CSS from IE-era selectors. Modern features are all progressive: oklch() (Chrome 111 / Safari 15.4 / Firefox 113) sits behind @supports over a hex baseline, color-mix() (Chrome 111 / Safari 16.2 / Firefox 113) only tints the header wash, and scrollbar-gutter (Chrome 94 / Firefox 97, not Safari) only prevents a reflow. text-wrap: pretty is Chrome 117+ and cosmetic.

Techniques used in this demo

scrollbar-gutter / -width / -colorMDN ↗backdrop-filterMDN ↗:has()MDN ↗radial-gradient()MDN ↗color-mix()MDN ↗clamp()MDN ↗