Tailwind + JSMIT licensed

Tailwind CSS Centre-Origin Balance Slider for Audio Pan Control

A pan control anchored at zero: the fill grows left or right from the midpoint in opposing channel colours, a 24-bar visualiser leans with it, and a centre detent snaps the last few units back to dead centre. Both fills are one expression each — max() and clamp() do what an if/else chain did.

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The code

<section class="trs-13 w-full min-h-svh grid place-items-center bg-trs13-bg font-trs13-sans px-5 py-10" id="trs-13-root" style="--p:0">
  <div class="w-[min(470px,100%)] rounded-3xl bg-trs13-card border border-trs13-edge p-9 shadow-[0_24px_70px_-28px_oklch(0_0_0/0.8)]">
    <header class="text-center mb-8">
      <h3 class="text-lg font-bold text-trs13-ink m-0">Audio pan control</h3>
      <p class="text-[13px] text-trs13-mut mt-1 m-0">Drag from centre to pan left or right</p>
    </header>

    <div class="flex items-center justify-between gap-4 mb-6">
      <div class="text-center">
        <div class="text-[10px] uppercase tracking-[0.18em] text-trs13-mut">Left</div>
        <div class="font-trs13-mono text-[28px] font-semibold tracking-tight tabular-nums text-trs13-left" id="trs-13-left">50%</div>
      </div>
      <div class="flex flex-col items-center gap-1" id="trs-13-centre" data-centred="true">
        <span class="size-2.5 rounded-full bg-trs13-centre shadow-[0_0_8px_var(--color-trs13-centre)] opacity-30 transition-opacity duration-300 data-[centred=true]:opacity-100 motion-reduce:transition-none" id="trs-13-dot" data-centred="true"></span>
        <span class="text-[10px] font-semibold tracking-wider text-trs13-centre">C</span>
      </div>
      <div class="text-center">
        <div class="text-[10px] uppercase tracking-[0.18em] text-trs13-mut">Right</div>
        <div class="font-trs13-mono text-[28px] font-semibold tracking-tight tabular-nums text-trs13-right" id="trs-13-right">50%</div>
      </div>
    </div>

    <div class="relative h-12 flex items-center mb-2">
      <div class="absolute inset-x-0 h-2 rounded-full bg-trs13-edge"></div>
      <span class="absolute left-1/2 -translate-x-1/2 w-0.5 h-5 bg-trs13-centre/60" aria-hidden="true"></span>
      <div class="absolute right-1/2 h-2 rounded-l-full bg-trs13-left shadow-[0_0_14px_-2px_var(--color-trs13-left)] w-[calc(max(0,-1*var(--p))*50%)]" aria-hidden="true"></div>
      <div class="absolute left-1/2 h-2 rounded-r-full bg-trs13-right shadow-[0_0_14px_-2px_var(--color-trs13-right)] w-[calc(max(0,var(--p))*50%)]" aria-hidden="true"></div>
      <input type="range" min="-100" max="100" value="0" id="trs-13-inp" aria-label="Stereo pan"
             class="absolute inset-0 w-full h-12 appearance-none bg-transparent outline-none cursor-pointer z-10 focus-visible:outline-2 focus-visible:outline-offset-2 focus-visible:outline-trs13-centre rounded-full">
    </div>

    <div class="flex justify-between text-[11px] font-semibold mb-7">
      <span class="text-trs13-left">◀ L</span>
      <span class="text-trs13-right">R ▶</span>
    </div>

    <div class="flex items-end gap-[3px] h-15" id="trs-13-vis" aria-hidden="true"></div>

    <button type="button" id="trs-13-reset" class="block w-full min-h-11 mt-5 rounded-xl border border-trs13-edge text-xs font-semibold uppercase tracking-[0.12em] text-trs13-mut transition-colors duration-200 hover:border-trs13-centre hover:text-trs13-centre focus-visible:outline-2 focus-visible:outline-offset-2 focus-visible:outline-trs13-centre motion-reduce:transition-none">⊙ Reset to centre</button>
  </div>
</section>
@import "tailwindcss";

@theme {
  --color-trs13-bg: #0a0f1e;
  --color-trs13-bg: oklch(0.17 0.03 262);
  --color-trs13-card: #111a2f;
  --color-trs13-card: oklch(0.22 0.035 262);
  --color-trs13-edge: #22304d;
  --color-trs13-edge: oklch(0.31 0.04 262);
  --color-trs13-left: #38bdf8;
  --color-trs13-left: oklch(0.75 0.14 225);
  --color-trs13-right: #fb7185;
  --color-trs13-right: oklch(0.72 0.17 15);
  --color-trs13-centre: #a3e635;
  --color-trs13-centre: oklch(0.85 0.19 125);
  --color-trs13-ink: #e2e8f0;
  --color-trs13-ink: oklch(0.92 0.01 255);
  --color-trs13-mut: #7c8ba6;
  --color-trs13-mut: oklch(0.63 0.03 255);
  --font-trs13-sans: 'Space Grotesk', system-ui, sans-serif;
  --font-trs13-mono: 'JetBrains Mono', ui-monospace, monospace;
}

@property --p {
  syntax: "<number>";
  inherits: true;
  initial-value: 0;
}

.trs-13 {
  width: 100%;
  min-height: 100svh;
  transition: --p 75ms linear;
}

@media (prefers-reduced-motion: reduce) {
  .trs-13 {
    transition: none;
  }
}

.trs-13 input[type="range"]::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 28px;
  height: 28px;
  border-radius: 9999px;
  box-sizing: border-box;
  background: var(--color-trs13-edge);
  border: 3px solid var(--color-trs13-ink);
  box-shadow: 0 4px 16px oklch(0 0 0 / 0.55);
  cursor: grab;
  transition: transform .15s;
}

.trs-13 input[type="range"]:active::-webkit-slider-thumb {
  transform: scale(1.14);
  cursor: grabbing;
}

.trs-13 input[type="range"]::-moz-range-thumb {
  width: 28px;
  height: 28px;
  border-radius: 9999px;
  box-sizing: border-box;
  background: var(--color-trs13-edge);
  border: 3px solid var(--color-trs13-ink);
  cursor: grab;
}

@media (prefers-reduced-motion: reduce) {
  .trs-13 input[type="range"]::-webkit-slider-thumb {
    transition: none;
  }

  .trs-13 input[type="range"]:active::-webkit-slider-thumb {
    transform: none;
  }
}
(function(){
  var root = document.getElementById('trs-13-root');
  var inp = document.getElementById('trs-13-inp');
  var dot = document.getElementById('trs-13-dot');
  var vis = document.getElementById('trs-13-vis');
  var leftPct = document.getElementById('trs-13-left');
  var rightPct = document.getElementById('trs-13-right');
  var BARS = 24, DETENT = 5;

  for (var i = 0; i < BARS; i++) {
    var b = document.createElement('span');
    b.className = 'flex-1 rounded-t-sm transition-[height,opacity] duration-150 motion-reduce:transition-none ' + (i < BARS / 2 ? 'bg-trs13-left' : 'bg-trs13-right');
    vis.appendChild(b);
    if (i === BARS / 2 - 1) {
      var d = document.createElement('span');
      d.className = 'w-0.5 h-full shrink-0 bg-trs13-centre/30';
      vis.appendChild(d);
    }
  }
  var bars = Array.prototype.slice.call(vis.querySelectorAll('span:not(.w-0\\.5)'));

  function update(){
    var v = +inp.value;
    if (Math.abs(v) <= DETENT && v !== 0) { v = 0; inp.value = 0; }
    root.style.setProperty('--p', v / 100);
    var l = Math.round(50 - v / 2), r = Math.round(50 + v / 2);
    leftPct.textContent = l + '%';
    rightPct.textContent = r + '%';
    dot.dataset.centred = v === 0 ? 'true' : 'false';
    inp.setAttribute('aria-valuetext', v === 0 ? 'Centred' : Math.abs(v) + '% ' + (v < 0 ? 'left' : 'right'));
    var half = BARS / 2, mag = Math.abs(v);
    bars.forEach(function(bar, i){
      var isLeft = i < half;
      var dist = isLeft ? (half - 1 - i) : (i - half);
      var h;
      if ((v < 0 && isLeft) || (v > 0 && !isLeft)) h = 10 + (dist / (half - 1)) * mag * 0.5;
      else if (v === 0) h = 10 + (1 - dist / half) * 20;
      else h = 8;
      bar.style.height = Math.min(60, h) + 'px';
      bar.style.opacity = String(0.3 + Math.min(60, h) / 60 * 0.7);
    });
  }
  inp.addEventListener('input', update);
  document.getElementById('trs-13-reset').addEventListener('click', function(){ inp.value = 0; update(); });
  update();
})();

Setup — do this once per project

Skip this if your project already runs Tailwind v4.

1Load Tailwind
<script src="https://cdn.jsdelivr.net/npm/@tailwindcss/browser@4"></script>

Compiles in the browser — perfect for a CodePen or a quick test, not for production.

2Add the stylesheetRequiredthe @theme block is what makes the custom utilities exist
@import "tailwindcss";

@theme {
  --color-trs13-bg: #0a0f1e;
  --color-trs13-bg: oklch(0.17 0.03 262);
  --color-trs13-card: #111a2f;
  --color-trs13-card: oklch(0.22 0.035 262);
  --color-trs13-edge: #22304d;
  --color-trs13-edge: oklch(0.31 0.04 262);
  --color-trs13-left: #38bdf8;
  --color-trs13-left: oklch(0.75 0.14 225);
  --color-trs13-right: #fb7185;
  --color-trs13-right: oklch(0.72 0.17 15);
  --color-trs13-centre: #a3e635;
  --color-trs13-centre: oklch(0.85 0.19 125);
  --color-trs13-ink: #e2e8f0;
  --color-trs13-ink: oklch(0.92 0.01 255);
  --color-trs13-mut: #7c8ba6;
  --color-trs13-mut: oklch(0.63 0.03 255);
  --font-trs13-sans: 'Space Grotesk', system-ui, sans-serif;
  --font-trs13-mono: 'JetBrains Mono', ui-monospace, monospace;
}

@property --p {
  syntax: "<number>";
  inherits: true;
  initial-value: 0;
}

.trs-13 {
  width: 100%;
  min-height: 100svh;
  transition: --p 75ms linear;
}

@media (prefers-reduced-motion: reduce) {
  .trs-13 {
    transition: none;
  }
}

.trs-13 input[type="range"]::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 28px;
  height: 28px;
  border-radius: 9999px;
  box-sizing: border-box;
  background: var(--color-trs13-edge);
  border: 3px solid var(--color-trs13-ink);
  box-shadow: 0 4px 16px oklch(0 0 0 / 0.55);
  cursor: grab;
  transition: transform .15s;
}

.trs-13 input[type="range"]:active::-webkit-slider-thumb {
  transform: scale(1.14);
  cursor: grabbing;
}

.trs-13 input[type="range"]::-moz-range-thumb {
  width: 28px;
  height: 28px;
  border-radius: 9999px;
  box-sizing: border-box;
  background: var(--color-trs13-edge);
  border: 3px solid var(--color-trs13-ink);
  cursor: grab;
}

@media (prefers-reduced-motion: reduce) {
  .trs-13 input[type="range"]::-webkit-slider-thumb {
    transition: none;
  }

  .trs-13 input[type="range"]:active::-webkit-slider-thumb {
    transform: none;
  }
}
3Fonts used by this demooptional — skip if you have your own type stack
<link rel="preconnect" href="https://fonts.googleapis.com">
<link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
<link rel="stylesheet" href="https://fonts.googleapis.com/css2?family=Space+Grotesk:wght@400;600;700&family=JetBrains+Mono:wght@600&display=swap">

What changed in the port

Which parts became utilities, which stayed CSS, and why.

  • The three-branch fill logic became two mirrored calc(max(0,…)) widths, so the "both fills at zero" case is arithmetic rather than a code path that can be missed.
  • The centre dot's opacity moved from a JS assignment to data-[centred=true]:opacity-100.
  • UI upgrade: a ±5-unit centre detent, L/C/R aria-valuetext instead of a bare negative number, and a 44px reset button.
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 demo 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: Tailwind CSS Centre-Origin Balance Slider for Audio Pan Control
Source: https://codefronts.com/components/tailwind-css-range-sliders/tailwind-centre-origin-balance-slider-audio-pan/

A pan control anchored at zero: the fill grows left or right from the midpoint in opposing channel colours, a 24-bar visualiser leans with it, and a centre detent snaps the last few units back to dead centre. Both fills are one expression each — max() and clamp() do what an if/else chain did.
## HTML
```html
<section class="trs-13 w-full min-h-svh grid place-items-center bg-trs13-bg font-trs13-sans px-5 py-10" id="trs-13-root" style="--p:0">
  <div class="w-[min(470px,100%)] rounded-3xl bg-trs13-card border border-trs13-edge p-9 shadow-[0_24px_70px_-28px_oklch(0_0_0/0.8)]">
    <header class="text-center mb-8">
      <h3 class="text-lg font-bold text-trs13-ink m-0">Audio pan control</h3>
      <p class="text-[13px] text-trs13-mut mt-1 m-0">Drag from centre to pan left or right</p>
    </header>

    <div class="flex items-center justify-between gap-4 mb-6">
      <div class="text-center">
        <div class="text-[10px] uppercase tracking-[0.18em] text-trs13-mut">Left</div>
        <div class="font-trs13-mono text-[28px] font-semibold tracking-tight tabular-nums text-trs13-left" id="trs-13-left">50%</div>
      </div>
      <div class="flex flex-col items-center gap-1" id="trs-13-centre" data-centred="true">
        <span class="size-2.5 rounded-full bg-trs13-centre shadow-[0_0_8px_var(--color-trs13-centre)] opacity-30 transition-opacity duration-300 data-[centred=true]:opacity-100 motion-reduce:transition-none" id="trs-13-dot" data-centred="true"></span>
        <span class="text-[10px] font-semibold tracking-wider text-trs13-centre">C</span>
      </div>
      <div class="text-center">
        <div class="text-[10px] uppercase tracking-[0.18em] text-trs13-mut">Right</div>
        <div class="font-trs13-mono text-[28px] font-semibold tracking-tight tabular-nums text-trs13-right" id="trs-13-right">50%</div>
      </div>
    </div>

    <div class="relative h-12 flex items-center mb-2">
      <div class="absolute inset-x-0 h-2 rounded-full bg-trs13-edge"></div>
      <span class="absolute left-1/2 -translate-x-1/2 w-0.5 h-5 bg-trs13-centre/60" aria-hidden="true"></span>
      <div class="absolute right-1/2 h-2 rounded-l-full bg-trs13-left shadow-[0_0_14px_-2px_var(--color-trs13-left)] w-[calc(max(0,-1*var(--p))*50%)]" aria-hidden="true"></div>
      <div class="absolute left-1/2 h-2 rounded-r-full bg-trs13-right shadow-[0_0_14px_-2px_var(--color-trs13-right)] w-[calc(max(0,var(--p))*50%)]" aria-hidden="true"></div>
      <input type="range" min="-100" max="100" value="0" id="trs-13-inp" aria-label="Stereo pan"
             class="absolute inset-0 w-full h-12 appearance-none bg-transparent outline-none cursor-pointer z-10 focus-visible:outline-2 focus-visible:outline-offset-2 focus-visible:outline-trs13-centre rounded-full">
    </div>

    <div class="flex justify-between text-[11px] font-semibold mb-7">
      <span class="text-trs13-left">◀ L</span>
      <span class="text-trs13-right">R ▶</span>
    </div>

    <div class="flex items-end gap-[3px] h-15" id="trs-13-vis" aria-hidden="true"></div>

    <button type="button" id="trs-13-reset" class="block w-full min-h-11 mt-5 rounded-xl border border-trs13-edge text-xs font-semibold uppercase tracking-[0.12em] text-trs13-mut transition-colors duration-200 hover:border-trs13-centre hover:text-trs13-centre focus-visible:outline-2 focus-visible:outline-offset-2 focus-visible:outline-trs13-centre motion-reduce:transition-none">⊙ Reset to centre</button>
  </div>
</section>
```
## CSS
```css
@import "tailwindcss";

@theme {
  --color-trs13-bg: #0a0f1e;
  --color-trs13-bg: oklch(0.17 0.03 262);
  --color-trs13-card: #111a2f;
  --color-trs13-card: oklch(0.22 0.035 262);
  --color-trs13-edge: #22304d;
  --color-trs13-edge: oklch(0.31 0.04 262);
  --color-trs13-left: #38bdf8;
  --color-trs13-left: oklch(0.75 0.14 225);
  --color-trs13-right: #fb7185;
  --color-trs13-right: oklch(0.72 0.17 15);
  --color-trs13-centre: #a3e635;
  --color-trs13-centre: oklch(0.85 0.19 125);
  --color-trs13-ink: #e2e8f0;
  --color-trs13-ink: oklch(0.92 0.01 255);
  --color-trs13-mut: #7c8ba6;
  --color-trs13-mut: oklch(0.63 0.03 255);
  --font-trs13-sans: 'Space Grotesk', system-ui, sans-serif;
  --font-trs13-mono: 'JetBrains Mono', ui-monospace, monospace;
}

@property --p {
  syntax: "<number>";
  inherits: true;
  initial-value: 0;
}

.trs-13 {
  width: 100%;
  min-height: 100svh;
  transition: --p 75ms linear;
}

@media (prefers-reduced-motion: reduce) {
  .trs-13 {
    transition: none;
  }
}

.trs-13 input[type="range"]::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 28px;
  height: 28px;
  border-radius: 9999px;
  box-sizing: border-box;
  background: var(--color-trs13-edge);
  border: 3px solid var(--color-trs13-ink);
  box-shadow: 0 4px 16px oklch(0 0 0 / 0.55);
  cursor: grab;
  transition: transform .15s;
}

.trs-13 input[type="range"]:active::-webkit-slider-thumb {
  transform: scale(1.14);
  cursor: grabbing;
}

.trs-13 input[type="range"]::-moz-range-thumb {
  width: 28px;
  height: 28px;
  border-radius: 9999px;
  box-sizing: border-box;
  background: var(--color-trs13-edge);
  border: 3px solid var(--color-trs13-ink);
  cursor: grab;
}

@media (prefers-reduced-motion: reduce) {
  .trs-13 input[type="range"]::-webkit-slider-thumb {
    transition: none;
  }

  .trs-13 input[type="range"]:active::-webkit-slider-thumb {
    transform: none;
  }
}
```

## JavaScript
```js
(function(){
  var root = document.getElementById('trs-13-root');
  var inp = document.getElementById('trs-13-inp');
  var dot = document.getElementById('trs-13-dot');
  var vis = document.getElementById('trs-13-vis');
  var leftPct = document.getElementById('trs-13-left');
  var rightPct = document.getElementById('trs-13-right');
  var BARS = 24, DETENT = 5;

  for (var i = 0; i < BARS; i++) {
    var b = document.createElement('span');
    b.className = 'flex-1 rounded-t-sm transition-[height,opacity] duration-150 motion-reduce:transition-none ' + (i < BARS / 2 ? 'bg-trs13-left' : 'bg-trs13-right');
    vis.appendChild(b);
    if (i === BARS / 2 - 1) {
      var d = document.createElement('span');
      d.className = 'w-0.5 h-full shrink-0 bg-trs13-centre/30';
      vis.appendChild(d);
    }
  }
  var bars = Array.prototype.slice.call(vis.querySelectorAll('span:not(.w-0\\.5)'));

  function update(){
    var v = +inp.value;
    if (Math.abs(v) <= DETENT && v !== 0) { v = 0; inp.value = 0; }
    root.style.setProperty('--p', v / 100);
    var l = Math.round(50 - v / 2), r = Math.round(50 + v / 2);
    leftPct.textContent = l + '%';
    rightPct.textContent = r + '%';
    dot.dataset.centred = v === 0 ? 'true' : 'false';
    inp.setAttribute('aria-valuetext', v === 0 ? 'Centred' : Math.abs(v) + '% ' + (v < 0 ? 'left' : 'right'));
    var half = BARS / 2, mag = Math.abs(v);
    bars.forEach(function(bar, i){
      var isLeft = i < half;
      var dist = isLeft ? (half - 1 - i) : (i - half);
      var h;
      if ((v < 0 && isLeft) || (v > 0 && !isLeft)) h = 10 + (dist / (half - 1)) * mag * 0.5;
      else if (v === 0) h = 10 + (1 - dist / half) * 20;
      else h = 8;
      bar.style.height = Math.min(60, h) + 'px';
      bar.style.opacity = String(0.3 + Math.min(60, h) / 60 * 0.7);
    });
  }
  inp.addEventListener('input', update);
  document.getElementById('trs-13-reset').addEventListener('click', function(){ inp.value = 0; update(); });
  update();
})();
```

How this works

One signed property, two mirrored fills. The controller writes --p in the range −1…1. The left fill is anchored right-1/2 and sized by max(0, -1 × p); the right fill is anchored left-1/2 and sized by max(0, p). At zero both evaluate to 0 with no special case — the original needed three branches and could leave a fill stranded on a fast reversal.

The visualiser leans. 24 bars split by a centre divider; each bar's height grows with its distance from centre on the ACTIVE side and flattens on the other, so the shape reads as energy moving across the stereo field.

The detent is the upgrade. Within ±5 units the value snaps to 0 and the centre dot lights, which is how hardware pan pots behave and what makes "back to centre" achievable with a drag.

Make it yours

  • Channel colours: --color-trs13-left / -right drive fills, labels, bars and glow.
  • Detent width: the DETENT constant; set it to 0 for a continuous sweep.
  • Web Audio: new StereoPannerNode(ctx, { pan: p }) and set pan.value = p on update.

Gotchas — read before shipping

  • The left fill grows leftward from right-1/2. Re-anchoring it to left-0 breaks the maths — the two fills are mirror images by construction.
  • Always coerce the value (+input.value): a string "0" is truthy and === 0 fails, which is the classic centre-detection bug here.
  • The bar count and the divider index must stay in sync — both derive from BARS in the controller.

Browser support

ChromeSafariFirefoxEdge
111+16.4+128+111+

max() inside a width calc() is Baseline; the mirrored-fill technique needs no prefixes.

Techniques used in this demo

Utilitiesfirst-class utility or variant

Theme tokensset in @theme, used by a utility

Plain CSSno Tailwind surface

HTML & JSno Tailwind involved

Search CodeFronts

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