22 CSS Headers14 / 22

Pure CSSMIT licensed

Flexbox Three Column Navbar Header

The reference implementation: logo left, nav optically centred, actions right — and it stays centred even when the logo and the button are wildly different widths. The trick is giving the outer columns equal flex-basis and letting the nav claim the middle, rather than trusting space-between. Monochrome Swiss treatment, hairline rules, zero decoration.

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The code

<div class="hd-14">
  <a class="hd-14__skip" href="#hd-14-main">Skip to content</a>

  <header class="hd-14__bar">
    <div class="hd-14__side hd-14__side--start">
      <a class="hd-14__brand" href="#hd-14-main">
        <svg class="hd-14__mark" viewBox="0 0 24 24" fill="none" aria-hidden="true" focusable="false">
          <rect x="3.5" y="3.5" width="7" height="7" fill="currentColor"/>
          <rect x="13.5" y="3.5" width="7" height="7" stroke="currentColor" stroke-width="1.6"/>
          <rect x="3.5" y="13.5" width="7" height="7" stroke="currentColor" stroke-width="1.6"/>
          <rect x="13.5" y="13.5" width="7" height="7" fill="currentColor"/>
        </svg>
        <span class="hd-14__word">Grid &amp; Rule</span>
      </a>
    </div>

    <nav class="hd-14__nav" aria-label="Main">
      <ul>
        <li><a href="#hd-14-main" aria-current="page">Work</a></li>
        <li><a href="#hd-14-main">Studio</a></li>
        <li><a href="#hd-14-main">Writing</a></li>
        <li><a href="#hd-14-main">Contact</a></li>
      </ul>
    </nav>

    <div class="hd-14__side hd-14__side--end">
      <input class="hd-14__sr" type="checkbox" id="hd-14-dark">
      <label class="hd-14__theme" for="hd-14-dark">
        <svg class="hd-14__sun" viewBox="0 0 24 24" fill="none" aria-hidden="true" focusable="false"><circle cx="12" cy="12" r="4.2" stroke="currentColor" stroke-width="1.8"/><path d="M12 2.8v2.1M12 19.1v2.1M2.8 12h2.1M19.1 12h2.1M5.5 5.5 7 7M17 17l1.5 1.5M18.5 5.5 17 7M7 17l-1.5 1.5" stroke="currentColor" stroke-width="1.7" stroke-linecap="round"/></svg>
        <svg class="hd-14__moon" viewBox="0 0 24 24" fill="none" aria-hidden="true" focusable="false"><path d="M20.5 14.4A8.4 8.4 0 0 1 9.6 3.5 8.6 8.6 0 1 0 20.5 14.4Z" stroke="currentColor" stroke-width="1.8" stroke-linejoin="round"/></svg>
        <span class="hd-14__vh">Switch light or dark theme</span>
      </label>
      <input class="hd-14__sr" type="checkbox" id="hd-14-guides">
      <label class="hd-14__guide-btn" for="hd-14-guides">Show tracks</label>
      <a class="hd-14__cta" href="#hd-14-main">Start a project</a>
    </div>
  </header>

  <main class="hd-14__main" id="hd-14-main">
    <p class="hd-14__eyebrow">Layout reference &middot; 01</p>
    <h1>Three columns, one centred nav, no drift.</h1>
    <p class="hd-14__lead">Toggle <strong>Show tracks</strong> in the header to outline the flex columns. The side columns share slack equally, so the navigation stays optically centred no matter how long the wordmark or the button gets.</p>

    <div class="hd-14__code">
      <p class="hd-14__code-h">The whole layout</p>
      <pre><code>.bar   { display:flex; align-items:center; }
.side  { flex:1 1 0; min-inline-size:0; }
.side--start { justify-content:flex-start; }
.side--end   { justify-content:flex-end;   }
.nav   { flex:0 1 auto; }</code></pre>
    </div>

    <dl class="hd-14__notes">
      <div><dt>flex-basis: 0</dt><dd>Both sides start from zero, so growth is symmetrical and the middle track is the true centre.</dd></div>
      <div><dt>min-inline-size: 0</dt><dd>Lets a long wordmark truncate instead of setting a floor for the whole row.</dd></div>
      <div><dt>flex: 0 1 auto</dt><dd>The nav keeps its natural width and only shrinks when there is genuinely no room.</dd></div>
    </dl>
    <div class="hd-14__filler" aria-hidden="true"></div>
  </main>
</div>
.hd-14 {
  --paper: #ffffff;
  --paper2: #f5f5f5;
  --ink: #0a0a0a;
  --muted: #6b6b6b;
  --line: #0a0a0a;
  --hair: rgba(10,10,10,.14);
  --guide: #0a0a0a;
  --track: .14em;
  --bar-h: 4.25rem;
  --font-display: system-ui,-apple-system,"Helvetica Neue",Helvetica,sans-serif;
  --font-body: system-ui,-apple-system,"Segoe UI",sans-serif;
  width: 100%;
  min-height: 100vh;
  display: block;
  background-color: var(--paper);
  background-image: repeating-linear-gradient(to bottom, var(--hair) 0 1px, transparent 1px 8px);
  background-size: 100% 8px;
  color: var(--ink);
  font-family: var(--font-body);
  line-height: 1.55;
}

@supports (color: oklch(50% .1 200)) {
  .hd-14 {
    --paper: oklch(100% 0 0);
    --paper2: oklch(96% 0 0);
    --ink: oklch(12% 0 0);
    --muted: oklch(50% 0 0);
  }
}

.hd-14 * {
  box-sizing: border-box;
}

.hd-14 h1,
.hd-14 p,
.hd-14 ul,
.hd-14 dl,
.hd-14 dt,
.hd-14 dd,
.hd-14 pre {
  margin: 0;
  padding: 0;
}

.hd-14 ul {
  list-style: none;
}

.hd-14 [hidden] {
  display: none;
}

.hd-14 :focus-visible {
  outline: 2px solid var(--ink);
  outline-offset: 3px;
}

.hd-14__sr {
  position: absolute;
  inline-size: 1px;
  block-size: 1px;
  overflow: hidden;
  clip-path: inset(50%);
}

.hd-14__skip {
  position: absolute;
  inset-inline-start: 1rem;
  top: -3rem;
  z-index: 60;
  padding: .5rem .9rem;
  background: var(--ink);
  color: var(--paper);
  font-size: .76rem;
  font-weight: 700;
  letter-spacing: .1em;
  text-transform: uppercase;
  text-decoration: none;
  transition: top .18s ease;
}

.hd-14__skip:focus-visible {
  top: .75rem;
}
/* ── the three-column flex header ─────────────────────────────────── */

.hd-14__bar {
  position: sticky;
  top: 0;
  z-index: 30;
  display: flex;
  align-items: center;
  gap: 1rem;
  min-block-size: var(--bar-h);
  padding-inline: clamp(1rem,4vw,2.5rem);
  background: var(--paper);
  border-bottom: 1px solid var(--line);
}

.hd-14__side {
  display: flex;
  align-items: center;
  gap: .75rem;
  flex: 1 1 0;
  min-inline-size: 0;
}

.hd-14__side--start {
  justify-content: flex-start;
}

.hd-14__side--end {
  justify-content: flex-end;
}

.hd-14__nav {
  flex: 0 1 auto;
  min-inline-size: 0;
}

.hd-14__brand {
  display: inline-flex;
  align-items: center;
  gap: .55rem;
  color: var(--ink);
  text-decoration: none;
  min-inline-size: 0;
}

.hd-14__mark {
  inline-size: 1.4rem;
  block-size: 1.4rem;
  flex: none;
}

.hd-14__word {
  font-family: var(--font-display);
  font-size: .8rem;
  font-weight: 700;
  letter-spacing: .2em;
  text-transform: uppercase;
  min-inline-size: 0;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.hd-14__nav ul {
  display: flex;
  align-items: center;
  gap: clamp(1rem,3vw,2rem);
}

.hd-14__nav a {
  display: block;
  padding: .5rem 0;
  color: var(--muted);
  text-decoration: none;
  font-size: .76rem;
  font-weight: 640;
  letter-spacing: var(--track);
  text-transform: uppercase;
  white-space: nowrap;
  border-bottom: 1px solid transparent;
  transition: color .16s ease, border-color .16s ease;
}

.hd-14__nav a:hover {
  color: var(--ink);
  border-bottom-color: var(--ink);
}

.hd-14__nav a[aria-current="page"] {
  color: var(--ink);
  border-bottom-color: var(--ink);
}

.hd-14__guide-btn {
  padding: .5rem .75rem;
  border: 1px solid var(--hair);
  color: var(--muted);
  font-size: .68rem;
  font-weight: 700;
  letter-spacing: .12em;
  text-transform: uppercase;
  cursor: pointer;
  white-space: nowrap;
  transition: color .16s ease, border-color .16s ease;
}

.hd-14__guide-btn:hover {
  color: var(--ink);
  border-color: var(--ink);
}

.hd-14:has(#hd-14-guides:checked) .hd-14__guide-btn {
  background: var(--ink);
  color: var(--paper);
  border-color: var(--ink);
}

.hd-14:has(#hd-14-guides:focus-visible) .hd-14__guide-btn {
  outline: 2px solid var(--ink);
  outline-offset: 2px;
}

.hd-14:has(#hd-14-guides:checked) .hd-14__side,
.hd-14:has(#hd-14-guides:checked) .hd-14__nav {
  outline: 1px dashed var(--guide);
  outline-offset: -1px;
  position: relative;
}

.hd-14:has(#hd-14-guides:checked) .hd-14__side::after,
.hd-14:has(#hd-14-guides:checked) .hd-14__nav::after {
  content: attr(data-track);
  position: absolute;
  top: .1rem;
  inset-inline-start: .15rem;
  font-size: .55rem;
  font-weight: 700;
  letter-spacing: .1em;
  text-transform: uppercase;
  color: var(--muted);
}

.hd-14__cta {
  display: inline-flex;
  align-items: center;
  min-block-size: 2.5rem;
  padding: .6rem 1.1rem;
  background: var(--ink);
  color: var(--paper);
  text-decoration: none;
  font-size: .72rem;
  font-weight: 700;
  letter-spacing: .12em;
  text-transform: uppercase;
  white-space: nowrap;
  transition: opacity .16s ease;
}

.hd-14__cta:hover {
  opacity: .82;
}
/* ── page body ────────────────────────────────────────────────────── */

.hd-14__main {
  max-inline-size: 62rem;
  margin-inline: auto;
  padding: clamp(2.5rem,7vw,4.5rem) clamp(1rem,4vw,2.5rem) 5rem;
}

.hd-14__eyebrow {
  font-size: .7rem;
  font-weight: 700;
  letter-spacing: .2em;
  text-transform: uppercase;
  color: var(--muted);
}

.hd-14__main h1 {
  font-family: var(--font-display);
  font-size: clamp(1.9rem,6vw,3.2rem);
  line-height: 1.05;
  font-weight: 700;
  letter-spacing: -.04em;
  margin-top: 1rem;
  max-inline-size: 24ch;
  text-wrap: balance;
}

.hd-14__lead {
  margin-top: 1.1rem;
  max-inline-size: 56ch;
  color: var(--muted);
  font-size: 1.02rem;
  text-wrap: pretty;
}

.hd-14__code {
  margin-top: 2.25rem;
  border: 1px solid var(--line);
  background: var(--paper);
}

.hd-14__code-h {
  padding: .6rem .9rem;
  border-bottom: 1px solid var(--line);
  font-size: .68rem;
  font-weight: 700;
  letter-spacing: .14em;
  text-transform: uppercase;
  color: var(--muted);
}

.hd-14__code pre {
  padding: 1rem .9rem;
  overflow: auto;
  font-family: ui-monospace,Menlo,"Courier New",monospace;
  font-size: .84rem;
  line-height: 1.75;
}

.hd-14__notes {
  display: grid;
  gap: 0;
  margin-top: 2rem;
  border-top: 1px solid var(--line);
}

.hd-14__notes > div {
  display: grid;
  grid-template-columns: 14rem minmax(0,1fr);
  gap: 1.5rem;
  padding: .9rem .1rem;
  border-bottom: 1px solid var(--hair);
}

.hd-14__notes dt {
  font-family: ui-monospace,Menlo,monospace;
  font-size: .82rem;
  font-weight: 600;
}

.hd-14__notes dd {
  font-size: .9rem;
  color: var(--muted);
  text-wrap: pretty;
}

.hd-14__filler {
  block-size: 45vh;
}

@media (max-width: 720px) {
  .hd-14__bar {
    flex-wrap: wrap;
    padding-block: .75rem;
    gap: .6rem;
  }

  .hd-14__side {
    flex: 1 1 auto;
  }

  .hd-14__nav {
    order: 3;
    flex-basis: 100%;
    justify-content: center;
    display: flex;
  }

  .hd-14__nav ul {
    justify-content: center;
    flex-wrap: wrap;
  }

  .hd-14__guide-btn {
    display: none;
  }

  .hd-14__notes > div {
    grid-template-columns: minmax(0,1fr);
    gap: .25rem;
  }
}
/* ── manual theme toggle — beats the OS default ──────────────────── */

.hd-14:has(#hd-14-dark:checked) {
  --paper: #0a0a0a;
  --paper2: #151515;
  --ink: #f5f5f5;
  --muted: #9b9b9b;
  --line: #f5f5f5;
  --hair: rgba(245,245,245,.14);
  --guide: #f5f5f5;
}

.hd-14:has(#hd-14-dark:checked) {
  background-image: repeating-linear-gradient(to bottom, rgba(245,245,245,.1) 0 1px, transparent 1px 8px);
}
/* icon: shows the scheme the toggle will switch you to */

.hd-14__sun {
  display: none;
}

.hd-14:has(#hd-14-dark:checked) .hd-14__moon {
  display: none;
}

.hd-14:has(#hd-14-dark:checked) .hd-14__sun {
  display: block;
}

@media (prefers-color-scheme: dark) {
  .hd-14:not([data-theme="light"]):not(:has(#hd-14-dark:checked)):not(:has(#hd-14-dark:checked)) {
    --paper: #0a0a0a;
    --paper2: #151515;
    --ink: #f5f5f5;
    --muted: #9b9b9b;
    --line: #f5f5f5;
    --hair: rgba(245,245,245,.14);
    --guide: #f5f5f5;
  }

  .hd-14:not([data-theme="light"]) {
    background-image: repeating-linear-gradient(to bottom, rgba(245,245,245,.1) 0 1px, transparent 1px 8px);
  }
  /* FLIP-BACK — dark OS + checked toggle returns to the other scheme */

  .hd-14:has(#hd-14-dark:checked) {
    --paper: #ffffff;
    --paper2: #f5f5f5;
    --ink: #0a0a0a;
    --muted: #6b6b6b;
    --line: #0a0a0a;
    --hair: rgba(10,10,10,.14);
    --guide: #0a0a0a;
    --track: .14em;
    --bar-h: 4.25rem;
    --font-display: system-ui,-apple-system,"Helvetica Neue",Helvetica,sans-serif;
    --font-body: system-ui,-apple-system,"Segoe UI",sans-serif;
  }
  /* the icon always offers the scheme you are not in */

  .hd-14:not([data-theme="light"]):not(:has(#hd-14-dark:checked)) .hd-14__moon {
    display: none;
  }

  .hd-14:not([data-theme="light"]):not(:has(#hd-14-dark:checked)) .hd-14__sun {
    display: block;
  }

  .hd-14:has(#hd-14-dark:checked) .hd-14__sun {
    display: none;
  }

  .hd-14:has(#hd-14-dark:checked) .hd-14__moon {
    display: block;
  }
}

.hd-14[data-theme="dark"] {
  --paper: #0a0a0a;
  --paper2: #151515;
  --ink: #f5f5f5;
  --muted: #9b9b9b;
  --line: #f5f5f5;
  --hair: rgba(245,245,245,.14);
  --guide: #f5f5f5;
}

@media (prefers-reduced-motion: reduce) {
  .hd-14 * {
    transition-duration: 1ms !important;
  }
}

@media (forced-colors: active) {
  .hd-14__cta {
    border: 1px solid CanvasText;
  }
}
/* ── theme toggle — visually hidden checkbox, zero JS ────────────── */

.hd-14__vh {
  position: absolute;
  inline-size: 1px;
  block-size: 1px;
  overflow: hidden;
  clip-path: inset(50%);
  white-space: nowrap;
}

.hd-14__theme {
  display: grid;
  place-items: center;
  inline-size: 2.75rem;
  block-size: 2.75rem;
  border: 0;
  border-radius: 999px;
  background: transparent;
  color: inherit;
  cursor: pointer;
  transition: background-color .18s ease;
}

.hd-14__theme svg {
  inline-size: 1.15rem;
  block-size: 1.15rem;
}

.hd-14__theme:hover {
  background: rgba(128,128,128,.16);
}

.hd-14:has(#hd-14-dark:focus-visible) .hd-14__theme {
  outline: 2px solid currentColor;
  outline-offset: 2px;
}
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 Header 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: Flexbox Three Column Navbar Header
Source: https://codefronts.com/layouts/css-header-designs/flexbox-3-column-navbar-header/

The reference implementation: logo left, nav optically centred, actions right &mdash; and it stays centred even when the logo and the button are wildly different widths. The trick is giving the outer columns equal flex-basis and letting the nav claim the middle, rather than trusting space-between. Monochrome Swiss treatment, hairline rules, zero decoration.
## HTML
```html
<div class="hd-14">
  <a class="hd-14__skip" href="#hd-14-main">Skip to content</a>

  <header class="hd-14__bar">
    <div class="hd-14__side hd-14__side--start">
      <a class="hd-14__brand" href="#hd-14-main">
        <svg class="hd-14__mark" viewBox="0 0 24 24" fill="none" aria-hidden="true" focusable="false">
          <rect x="3.5" y="3.5" width="7" height="7" fill="currentColor"/>
          <rect x="13.5" y="3.5" width="7" height="7" stroke="currentColor" stroke-width="1.6"/>
          <rect x="3.5" y="13.5" width="7" height="7" stroke="currentColor" stroke-width="1.6"/>
          <rect x="13.5" y="13.5" width="7" height="7" fill="currentColor"/>
        </svg>
        <span class="hd-14__word">Grid &amp; Rule</span>
      </a>
    </div>

    <nav class="hd-14__nav" aria-label="Main">
      <ul>
        <li><a href="#hd-14-main" aria-current="page">Work</a></li>
        <li><a href="#hd-14-main">Studio</a></li>
        <li><a href="#hd-14-main">Writing</a></li>
        <li><a href="#hd-14-main">Contact</a></li>
      </ul>
    </nav>

    <div class="hd-14__side hd-14__side--end">
      <input class="hd-14__sr" type="checkbox" id="hd-14-dark">
      <label class="hd-14__theme" for="hd-14-dark">
        <svg class="hd-14__sun" viewBox="0 0 24 24" fill="none" aria-hidden="true" focusable="false"><circle cx="12" cy="12" r="4.2" stroke="currentColor" stroke-width="1.8"/><path d="M12 2.8v2.1M12 19.1v2.1M2.8 12h2.1M19.1 12h2.1M5.5 5.5 7 7M17 17l1.5 1.5M18.5 5.5 17 7M7 17l-1.5 1.5" stroke="currentColor" stroke-width="1.7" stroke-linecap="round"/></svg>
        <svg class="hd-14__moon" viewBox="0 0 24 24" fill="none" aria-hidden="true" focusable="false"><path d="M20.5 14.4A8.4 8.4 0 0 1 9.6 3.5 8.6 8.6 0 1 0 20.5 14.4Z" stroke="currentColor" stroke-width="1.8" stroke-linejoin="round"/></svg>
        <span class="hd-14__vh">Switch light or dark theme</span>
      </label>
      <input class="hd-14__sr" type="checkbox" id="hd-14-guides">
      <label class="hd-14__guide-btn" for="hd-14-guides">Show tracks</label>
      <a class="hd-14__cta" href="#hd-14-main">Start a project</a>
    </div>
  </header>

  <main class="hd-14__main" id="hd-14-main">
    <p class="hd-14__eyebrow">Layout reference &middot; 01</p>
    <h1>Three columns, one centred nav, no drift.</h1>
    <p class="hd-14__lead">Toggle <strong>Show tracks</strong> in the header to outline the flex columns. The side columns share slack equally, so the navigation stays optically centred no matter how long the wordmark or the button gets.</p>

    <div class="hd-14__code">
      <p class="hd-14__code-h">The whole layout</p>
      <pre><code>.bar   { display:flex; align-items:center; }
.side  { flex:1 1 0; min-inline-size:0; }
.side--start { justify-content:flex-start; }
.side--end   { justify-content:flex-end;   }
.nav   { flex:0 1 auto; }</code></pre>
    </div>

    <dl class="hd-14__notes">
      <div><dt>flex-basis: 0</dt><dd>Both sides start from zero, so growth is symmetrical and the middle track is the true centre.</dd></div>
      <div><dt>min-inline-size: 0</dt><dd>Lets a long wordmark truncate instead of setting a floor for the whole row.</dd></div>
      <div><dt>flex: 0 1 auto</dt><dd>The nav keeps its natural width and only shrinks when there is genuinely no room.</dd></div>
    </dl>
    <div class="hd-14__filler" aria-hidden="true"></div>
  </main>
</div>
```
## CSS
```css
.hd-14 {
  --paper: #ffffff;
  --paper2: #f5f5f5;
  --ink: #0a0a0a;
  --muted: #6b6b6b;
  --line: #0a0a0a;
  --hair: rgba(10,10,10,.14);
  --guide: #0a0a0a;
  --track: .14em;
  --bar-h: 4.25rem;
  --font-display: system-ui,-apple-system,"Helvetica Neue",Helvetica,sans-serif;
  --font-body: system-ui,-apple-system,"Segoe UI",sans-serif;
  width: 100%;
  min-height: 100vh;
  display: block;
  background-color: var(--paper);
  background-image: repeating-linear-gradient(to bottom, var(--hair) 0 1px, transparent 1px 8px);
  background-size: 100% 8px;
  color: var(--ink);
  font-family: var(--font-body);
  line-height: 1.55;
}

@supports (color: oklch(50% .1 200)) {
  .hd-14 {
    --paper: oklch(100% 0 0);
    --paper2: oklch(96% 0 0);
    --ink: oklch(12% 0 0);
    --muted: oklch(50% 0 0);
  }
}

.hd-14 * {
  box-sizing: border-box;
}

.hd-14 h1,
.hd-14 p,
.hd-14 ul,
.hd-14 dl,
.hd-14 dt,
.hd-14 dd,
.hd-14 pre {
  margin: 0;
  padding: 0;
}

.hd-14 ul {
  list-style: none;
}

.hd-14 [hidden] {
  display: none;
}

.hd-14 :focus-visible {
  outline: 2px solid var(--ink);
  outline-offset: 3px;
}

.hd-14__sr {
  position: absolute;
  inline-size: 1px;
  block-size: 1px;
  overflow: hidden;
  clip-path: inset(50%);
}

.hd-14__skip {
  position: absolute;
  inset-inline-start: 1rem;
  top: -3rem;
  z-index: 60;
  padding: .5rem .9rem;
  background: var(--ink);
  color: var(--paper);
  font-size: .76rem;
  font-weight: 700;
  letter-spacing: .1em;
  text-transform: uppercase;
  text-decoration: none;
  transition: top .18s ease;
}

.hd-14__skip:focus-visible {
  top: .75rem;
}
/* ── the three-column flex header ─────────────────────────────────── */

.hd-14__bar {
  position: sticky;
  top: 0;
  z-index: 30;
  display: flex;
  align-items: center;
  gap: 1rem;
  min-block-size: var(--bar-h);
  padding-inline: clamp(1rem,4vw,2.5rem);
  background: var(--paper);
  border-bottom: 1px solid var(--line);
}

.hd-14__side {
  display: flex;
  align-items: center;
  gap: .75rem;
  flex: 1 1 0;
  min-inline-size: 0;
}

.hd-14__side--start {
  justify-content: flex-start;
}

.hd-14__side--end {
  justify-content: flex-end;
}

.hd-14__nav {
  flex: 0 1 auto;
  min-inline-size: 0;
}

.hd-14__brand {
  display: inline-flex;
  align-items: center;
  gap: .55rem;
  color: var(--ink);
  text-decoration: none;
  min-inline-size: 0;
}

.hd-14__mark {
  inline-size: 1.4rem;
  block-size: 1.4rem;
  flex: none;
}

.hd-14__word {
  font-family: var(--font-display);
  font-size: .8rem;
  font-weight: 700;
  letter-spacing: .2em;
  text-transform: uppercase;
  min-inline-size: 0;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.hd-14__nav ul {
  display: flex;
  align-items: center;
  gap: clamp(1rem,3vw,2rem);
}

.hd-14__nav a {
  display: block;
  padding: .5rem 0;
  color: var(--muted);
  text-decoration: none;
  font-size: .76rem;
  font-weight: 640;
  letter-spacing: var(--track);
  text-transform: uppercase;
  white-space: nowrap;
  border-bottom: 1px solid transparent;
  transition: color .16s ease, border-color .16s ease;
}

.hd-14__nav a:hover {
  color: var(--ink);
  border-bottom-color: var(--ink);
}

.hd-14__nav a[aria-current="page"] {
  color: var(--ink);
  border-bottom-color: var(--ink);
}

.hd-14__guide-btn {
  padding: .5rem .75rem;
  border: 1px solid var(--hair);
  color: var(--muted);
  font-size: .68rem;
  font-weight: 700;
  letter-spacing: .12em;
  text-transform: uppercase;
  cursor: pointer;
  white-space: nowrap;
  transition: color .16s ease, border-color .16s ease;
}

.hd-14__guide-btn:hover {
  color: var(--ink);
  border-color: var(--ink);
}

.hd-14:has(#hd-14-guides:checked) .hd-14__guide-btn {
  background: var(--ink);
  color: var(--paper);
  border-color: var(--ink);
}

.hd-14:has(#hd-14-guides:focus-visible) .hd-14__guide-btn {
  outline: 2px solid var(--ink);
  outline-offset: 2px;
}

.hd-14:has(#hd-14-guides:checked) .hd-14__side,
.hd-14:has(#hd-14-guides:checked) .hd-14__nav {
  outline: 1px dashed var(--guide);
  outline-offset: -1px;
  position: relative;
}

.hd-14:has(#hd-14-guides:checked) .hd-14__side::after,
.hd-14:has(#hd-14-guides:checked) .hd-14__nav::after {
  content: attr(data-track);
  position: absolute;
  top: .1rem;
  inset-inline-start: .15rem;
  font-size: .55rem;
  font-weight: 700;
  letter-spacing: .1em;
  text-transform: uppercase;
  color: var(--muted);
}

.hd-14__cta {
  display: inline-flex;
  align-items: center;
  min-block-size: 2.5rem;
  padding: .6rem 1.1rem;
  background: var(--ink);
  color: var(--paper);
  text-decoration: none;
  font-size: .72rem;
  font-weight: 700;
  letter-spacing: .12em;
  text-transform: uppercase;
  white-space: nowrap;
  transition: opacity .16s ease;
}

.hd-14__cta:hover {
  opacity: .82;
}
/* ── page body ────────────────────────────────────────────────────── */

.hd-14__main {
  max-inline-size: 62rem;
  margin-inline: auto;
  padding: clamp(2.5rem,7vw,4.5rem) clamp(1rem,4vw,2.5rem) 5rem;
}

.hd-14__eyebrow {
  font-size: .7rem;
  font-weight: 700;
  letter-spacing: .2em;
  text-transform: uppercase;
  color: var(--muted);
}

.hd-14__main h1 {
  font-family: var(--font-display);
  font-size: clamp(1.9rem,6vw,3.2rem);
  line-height: 1.05;
  font-weight: 700;
  letter-spacing: -.04em;
  margin-top: 1rem;
  max-inline-size: 24ch;
  text-wrap: balance;
}

.hd-14__lead {
  margin-top: 1.1rem;
  max-inline-size: 56ch;
  color: var(--muted);
  font-size: 1.02rem;
  text-wrap: pretty;
}

.hd-14__code {
  margin-top: 2.25rem;
  border: 1px solid var(--line);
  background: var(--paper);
}

.hd-14__code-h {
  padding: .6rem .9rem;
  border-bottom: 1px solid var(--line);
  font-size: .68rem;
  font-weight: 700;
  letter-spacing: .14em;
  text-transform: uppercase;
  color: var(--muted);
}

.hd-14__code pre {
  padding: 1rem .9rem;
  overflow: auto;
  font-family: ui-monospace,Menlo,"Courier New",monospace;
  font-size: .84rem;
  line-height: 1.75;
}

.hd-14__notes {
  display: grid;
  gap: 0;
  margin-top: 2rem;
  border-top: 1px solid var(--line);
}

.hd-14__notes > div {
  display: grid;
  grid-template-columns: 14rem minmax(0,1fr);
  gap: 1.5rem;
  padding: .9rem .1rem;
  border-bottom: 1px solid var(--hair);
}

.hd-14__notes dt {
  font-family: ui-monospace,Menlo,monospace;
  font-size: .82rem;
  font-weight: 600;
}

.hd-14__notes dd {
  font-size: .9rem;
  color: var(--muted);
  text-wrap: pretty;
}

.hd-14__filler {
  block-size: 45vh;
}

@media (max-width: 720px) {
  .hd-14__bar {
    flex-wrap: wrap;
    padding-block: .75rem;
    gap: .6rem;
  }

  .hd-14__side {
    flex: 1 1 auto;
  }

  .hd-14__nav {
    order: 3;
    flex-basis: 100%;
    justify-content: center;
    display: flex;
  }

  .hd-14__nav ul {
    justify-content: center;
    flex-wrap: wrap;
  }

  .hd-14__guide-btn {
    display: none;
  }

  .hd-14__notes > div {
    grid-template-columns: minmax(0,1fr);
    gap: .25rem;
  }
}
/* ── manual theme toggle — beats the OS default ──────────────────── */

.hd-14:has(#hd-14-dark:checked) {
  --paper: #0a0a0a;
  --paper2: #151515;
  --ink: #f5f5f5;
  --muted: #9b9b9b;
  --line: #f5f5f5;
  --hair: rgba(245,245,245,.14);
  --guide: #f5f5f5;
}

.hd-14:has(#hd-14-dark:checked) {
  background-image: repeating-linear-gradient(to bottom, rgba(245,245,245,.1) 0 1px, transparent 1px 8px);
}
/* icon: shows the scheme the toggle will switch you to */

.hd-14__sun {
  display: none;
}

.hd-14:has(#hd-14-dark:checked) .hd-14__moon {
  display: none;
}

.hd-14:has(#hd-14-dark:checked) .hd-14__sun {
  display: block;
}

@media (prefers-color-scheme: dark) {
  .hd-14:not([data-theme="light"]):not(:has(#hd-14-dark:checked)):not(:has(#hd-14-dark:checked)) {
    --paper: #0a0a0a;
    --paper2: #151515;
    --ink: #f5f5f5;
    --muted: #9b9b9b;
    --line: #f5f5f5;
    --hair: rgba(245,245,245,.14);
    --guide: #f5f5f5;
  }

  .hd-14:not([data-theme="light"]) {
    background-image: repeating-linear-gradient(to bottom, rgba(245,245,245,.1) 0 1px, transparent 1px 8px);
  }
  /* FLIP-BACK — dark OS + checked toggle returns to the other scheme */

  .hd-14:has(#hd-14-dark:checked) {
    --paper: #ffffff;
    --paper2: #f5f5f5;
    --ink: #0a0a0a;
    --muted: #6b6b6b;
    --line: #0a0a0a;
    --hair: rgba(10,10,10,.14);
    --guide: #0a0a0a;
    --track: .14em;
    --bar-h: 4.25rem;
    --font-display: system-ui,-apple-system,"Helvetica Neue",Helvetica,sans-serif;
    --font-body: system-ui,-apple-system,"Segoe UI",sans-serif;
  }
  /* the icon always offers the scheme you are not in */

  .hd-14:not([data-theme="light"]):not(:has(#hd-14-dark:checked)) .hd-14__moon {
    display: none;
  }

  .hd-14:not([data-theme="light"]):not(:has(#hd-14-dark:checked)) .hd-14__sun {
    display: block;
  }

  .hd-14:has(#hd-14-dark:checked) .hd-14__sun {
    display: none;
  }

  .hd-14:has(#hd-14-dark:checked) .hd-14__moon {
    display: block;
  }
}

.hd-14[data-theme="dark"] {
  --paper: #0a0a0a;
  --paper2: #151515;
  --ink: #f5f5f5;
  --muted: #9b9b9b;
  --line: #f5f5f5;
  --hair: rgba(245,245,245,.14);
  --guide: #f5f5f5;
}

@media (prefers-reduced-motion: reduce) {
  .hd-14 * {
    transition-duration: 1ms !important;
  }
}

@media (forced-colors: active) {
  .hd-14__cta {
    border: 1px solid CanvasText;
  }
}
/* ── theme toggle — visually hidden checkbox, zero JS ────────────── */

.hd-14__vh {
  position: absolute;
  inline-size: 1px;
  block-size: 1px;
  overflow: hidden;
  clip-path: inset(50%);
  white-space: nowrap;
}

.hd-14__theme {
  display: grid;
  place-items: center;
  inline-size: 2.75rem;
  block-size: 2.75rem;
  border: 0;
  border-radius: 999px;
  background: transparent;
  color: inherit;
  cursor: pointer;
  transition: background-color .18s ease;
}

.hd-14__theme svg {
  inline-size: 1.15rem;
  block-size: 1.15rem;
}

.hd-14__theme:hover {
  background: rgba(128,128,128,.16);
}

.hd-14:has(#hd-14-dark:focus-visible) .hd-14__theme {
  outline: 2px solid currentColor;
  outline-offset: 2px;
}
```

How this works

space-between does not centre anything. It distributes leftover space between items, so the nav sits at the midpoint of the gap — which moves whenever the logo or the button changes width. Equal outer columns fix the geometry:

.hd-14__bar{display:flex; align-items:center;}
.hd-14__side{flex:1 1 0; min-inline-size:0;}        /* equal, shrinkable */
.hd-14__side--start{justify-content:flex-start;}
.hd-14__side--end{justify-content:flex-end;}
.hd-14__nav{flex:0 1 auto;}                        /* natural width, centred */

flex: 1 1 0, not flex: 1 and not flex-grow: 1. The basis matters. With flex-basis: auto each column starts from its content width, so a wide button still steals space from the left column and the centre drifts. A zero basis makes both sides start equal and grow equally.

/* drift */  .hd-14__side{flex-grow:1;}        /* basis:auto */
/* centred */.hd-14__side{flex:1 1 0;}          /* basis:0   */

Toggle the guides to see it. A visually hidden checkbox plus :has(:checked) paints an outline on each flex track, so you can watch the centre column stay put while the side content changes length. It is the same technique as a theme toggle, used as a teaching aid — and it costs no script.

The trap: flex children that refuse to shrink. Every flex item defaults to min-width: auto, which means the longest word in the nav sets a floor for the whole row. At 360 px that floor pushes the actions column off-screen and gives the document a horizontal scrollbar. min-inline-size: 0 on the columns, plus text-overflow: ellipsis on the text, keeps everything inside the viewport.

Make it yours

  • Left-align the nav instead by changing the centre column's parent order — no other rule needs touching.
  • Change the tracking on nav links with --track; .14em reads Swiss, 0 reads neutral.
  • Swap the baseline grid off by removing the background-image on the root, or change its rhythm from 8px.
  • Add a third action by inserting into the end column — the centre stays centred because both sides still share slack equally.
  • Set --bar-h to match your product's chrome height; the guides and the rules follow it.
  • For a boxed layout, wrap the bar contents in a max-inline-size container and keep the flex rules identical.

Gotchas — read before shipping

  • justify-content: space-between centres the middle item only when the outer items happen to be the same width — it drifts in production the moment copy changes.
  • flex: 1 resolves to flex-basis: 0% but flex-grow: 1 alone leaves flex-basis: auto, which is the difference between centred and drifting.
  • Without min-inline-size: 0 on flex children, long nav labels force a horizontal scrollbar on the document at narrow widths.
  • Centring the nav with position: absolute; left: 50% centres against the header, not the remaining space, and it takes the nav out of flow so the side columns can overlap it.

Browser support

ChromeSafariFirefoxEdge
114+17.5+121+114+

Floor set by :has(), oklch(), text-wrap as this demo is written. The core technique itself goes back further — Chrome 88+.

Pure flexbox with no modern dependencies; the only enhancement is :has() (Chrome 105 / Safari 15.4 / Firefox 121) for the measure-guide toggle, which simply does nothing where unsupported.

Techniques used in this demo

:has()MDN ↗clip-pathMDN ↗text-wrap: prettyMDN ↗grid-templateMDN ↗clamp()MDN ↗place-items / place-contentMDN ↗

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