# Seat fill

Subtle web animation sketch from [https://mighil.com/animations](https://mighil.com/animations).

- **Live demo:** https://mighil.com/animations/seat-fill
- **Standalone HTML:** https://mighil.com/animations/seat-fill?download=1
- **This file:** https://mighil.com/animations/seat-fill/seat-fill.md
- **Technique:** `team`

## What it does

Empty seats fill in as people join.

## Instructions for AI / coding agents

Implement this micro-interaction in the user's stack (vanilla HTML, React, Vue, Svelte, etc.).

1. Use the **HTML** as the DOM structure (adapt JSX/templates as needed; keep class names and ids).
2. Include the **Theme** CSS (or map the same variables into the host design system). It switches light/dark with `prefers-color-scheme`.
3. Apply the **CSS** as-is when possible. It uses `var(--text-color)`, `var(--heading-color)`, `var(--background-color)`, etc. from the theme so both modes work.
4. Run the **JavaScript** after the markup mounts. Prefer `DOMContentLoaded` or a framework `useEffect` / `onMount`.
5. Keep motion respectful of `prefers-reduced-motion` if the snippet already checks it.
6. Do not depend on mighil.com runtime or fonts. Theme variables are enough for color.
7. If porting to a component, expose the interactive root via a ref and preserve accessibility attributes (`aria-*`, `role`, `button` types).

## Theme (auto light / dark)

```css
/* Auto light / dark — follows prefers-color-scheme */
:root{
  color-scheme: light dark;
  --text-color: hsl(0, 0%, 18%);
  --heading-color: hsl(0, 0%, 18%);
  --background-color: hsl(0, 0%, 99%);
  --bg-color: hsl(0, 0%, 99%);
  --link-color: hsl(0, 0%, 18%);
  --visited-color: hsl(0, 0%, 18%);
  --blockquote-color: hsl(0, 0%, 18%);
  --code-bg-color: hsl(0, 0%, 95%);
  --code-color: hsl(0, 0%, 18%);
  --sub-color: hsl(0, 0%, 29%);
}
@media (prefers-color-scheme: dark){
:root{
  --text-color: hsl(35, 25%, 85%);
  --heading-color: hsl(35.2, 32.6%, 82.5%);
  --background-color: hsl(60, 2.2%, 8.8%);
  --bg-color: hsl(60, 2.2%, 8.8%);
  --link-color: hsl(34.7, 55.3%, 79.8%);
  --visited-color: hsla(34.7, 55.3%, 79.8%, 0.85);
  --blockquote-color: hsl(35, 30%, 75%);
  --code-bg-color: hsl(30, 5%, 7.8%);
  --code-color: limegreen;
  --sub-color: hsla(34.7, 24.7%, 84.9%, 0.78);
}
}
```

## HTML

```html
<div class="seats" id="seats">
        <div class="seat is-on" data-seat="0">A</div>
        <div class="seat" data-seat="1">+</div>
        <div class="seat" data-seat="2">+</div>
        <div class="seat" data-seat="3">+</div>
        <span class="seat-label" id="seat-label">1 of 4</span>
      </div>
```

## CSS

```css
@keyframes scan-move{from{left:-30%}to{left:105%}}

@keyframes check-draw{to{stroke-dashoffset:0}}

@keyframes toast-drain{to{transform:scaleX(0)}}

@keyframes mic-ring{
  0%{opacity:.55;transform:scale(.9)}
  100%{opacity:0;transform:scale(1.55)}
}

.step-node.is-on{
  background:currentColor;border-color:currentColor;transform:scale(1.15);
}

.step-line.is-on > i{width:100%}

.scan:hover::after,.scan.is-on::after{opacity:1;animation:scan-move 2.4s ease-in-out infinite}

.tip-wrap:hover .tip-bubble,.tip-wrap:focus-within .tip-bubble,
.tip-wrap.is-on .tip-bubble{opacity:1;transform:translateX(-50%) translateY(0) scale(1)}

.snack.is-on{
  opacity:1;transform:translateY(0) scale(1);pointer-events:auto;max-height:64px;
  padding:10px 12px;border-width:1px;transition:opacity .28s ease,transform .35s cubic-bezier(.22,1,.36,1),max-height .3s ease,padding .3s ease;
}

.success-banner.is-on{opacity:1;transform:translateY(0);pointer-events:auto}

.success-banner.is-on path{animation:check-draw .35s ease forwards .1s}

.toast.is-on{opacity:1;transform:translateY(0);pointer-events:auto}

.toast.is-on .toast-timer > i{animation:toast-drain 3s linear forwards}

.stars button.is-preview,
.stars button.is-preview.is-on{
  color:var(--text-color);
}

.stars button.is-preview svg path,
.stars button.is-preview.is-on svg path{
  fill:currentColor;
  stroke:currentColor;
}

.stars button.is-on{
  color:color-mix(in srgb,#c9962a 88%,var(--text-color));
}

.stars button.is-on svg path{
  fill:color-mix(in srgb,#f0c14b 92%,#fff);
  stroke:color-mix(in srgb,#c9922a 90%,var(--text-color));
}

.wizard-dots span.is-on{background:currentColor}

.draft-banner.is-on{opacity:1;transform:translateY(0);pointer-events:auto}

.cmd-palette li.is-on{background:color-mix(in srgb,var(--text-color) 8%,transparent)}

.mic-btn.is-on{
  background:#c44;
  border-color:#c44;
  color:#fff;
}

.mic-btn.is-on::before,.mic-btn.is-on::after{
  border-color:#c44;
}

.mic-btn.is-on::before{animation:mic-ring 1.4s ease-out infinite}

.mic-btn.is-on::after{animation:mic-ring 1.4s ease-out infinite .45s}

.diff-pane.is-on .diff-add{grid-template-rows:1fr}

.diff-pane.is-on .diff-add > .diff-add-inner{
  opacity:1;transform:none;padding:4px 10px;
}

.slot.is-on{
  border-color:color-mix(in srgb,var(--text-color) 28%,transparent);
}

.slot.is-on > i{transform:scaleY(1)}

.slot.is-on > span{font-weight:600}

.bulk-row.is-on{
  border-color:color-mix(in srgb,var(--text-color) 22%,transparent);
  background:color-mix(in srgb,var(--text-color) 5%,transparent);
}

.bulk-row.is-on .bulk-check{
  border-color:color-mix(in srgb,var(--text-color) 55%,transparent);
  background:color-mix(in srgb,var(--text-color) 10%,transparent);
}

.bulk-row.is-on .bulk-check svg{opacity:1;transform:scale(1)}

.env-switch button.is-on{color:inherit}

.env-switch:not(.is-prod) button[data-env="staging"].is-on{color:color-mix(in srgb,#c90 75%,var(--text-color))}

.flag-row.is-on{
  border-color:color-mix(in srgb,#c90 40%,transparent);
  background:color-mix(in srgb,#c90 8%,transparent);
}

.flag-row.is-on .flag-meta span{color:color-mix(in srgb,#c90 70%,var(--text-color))}

.flag-sw[aria-checked="true"],
.flag-row.is-on .flag-sw{
  background:color-mix(in srgb,#c90 42%,transparent);
  border-color:color-mix(in srgb,#c90 50%,transparent);
}

.flag-sw[aria-checked="true"]::after,
.flag-row.is-on .flag-sw::after{transform:translateX(18px)}

.ws-item.is-on .ws-check{opacity:1;transform:scale(1)}

.unfurl.is-on .unfurl-card{
  grid-template-rows:1fr;opacity:1;
  border-color:color-mix(in srgb,var(--text-color) 12%,transparent);
}

.unfurl.is-on .unfurl-thumb{transform:none;opacity:1}

.seats{display:flex;align-items:center;gap:8px}

.seat{
  width:36px;height:36px;border-radius:50%;box-sizing:border-box;
  border:1.5px dashed color-mix(in srgb,var(--text-color) 22%,transparent);
  background:transparent;display:grid;place-items:center;
  font-size:.7rem;font-weight:600;color:color-mix(in srgb,var(--text-color) 40%,transparent);
  transition:border-color .25s ease,background .25s ease,color .2s ease,transform .3s cubic-bezier(.34,1.4,.64,1);
}

.seat.is-on{
  border-style:solid;border-color:transparent;
  background:color-mix(in srgb,var(--text-color) 14%,transparent);color:inherit;
  transform:scale(1.06);
}

.seat[data-seat="1"].is-on{background:color-mix(in srgb,#48a 28%,transparent)}

.seat[data-seat="2"].is-on{background:color-mix(in srgb,#a84 28%,transparent)}

.seat[data-seat="3"].is-on{background:color-mix(in srgb,#2a8 28%,transparent)}

.seat-label{font-size:.8rem;color:color-mix(in srgb,var(--text-color) 55%,transparent);margin-left:4px;min-width:4.5em}

.form-prog-field.is-on{
  border-color:color-mix(in srgb,#2a8 30%,transparent);
  background:color-mix(in srgb,#2a8 6%,transparent);
}

.form-prog-field.is-on svg{opacity:1;transform:scale(1)}

@media (prefers-reduced-motion: reduce){
  .breath-dot,.breath-ring,.wave.is-live span,.ink-drop,
  .marquee-track,
  .skel-line,.save-btn.is-loading .spin,.badge.is-bump,.like-btn.is-pop,.save-status.is-saving .dot,.stars button.is-pop svg,
  .field.is-invalid input,.save-btn.is-done .check path,.ux-check[aria-checked="true"] .ux-box path,.char-meta.is-warn,.success-banner.is-on path,
  .typing span,.conn-dot,.indet > i,.toast.is-on .toast-timer > i,.stagger-list.is-in .stagger-item,.submit-wrap.is-loading .submit-ring rect,.submit-wrap.is-settle,.hold-btn.is-settle,.confirm-btn.is-settle,.sync-btn.is-settle,.invite-btn.is-settle,.retry-btn.is-shake-err,.retry-btn.is-shake-ok,.cart-badge.is-pop,.mute-btn .x-line,.presence.is-ping .presence-dot::after,.tag-chip,.nudge-field.is-nudge,.tilt-scene:hover .tilt-tile::before,.demo-replay.is-tap,.hit.is-tap,.stack-toggle.is-tap,.nudge-btn.is-tap,.wipe.is-tap,.save-btn.is-tap,.copy-btn.is-tap,.like-btn.is-tap,.pin-btn.is-tap,.retry-btn.is-tap,.wizard-nav button.is-tap,.mute-btn.is-tap,
  .scan:hover::after,.scan.is-on::after,.cascade.is-in b,.stepper-val.is-bump,.otp input.is-pop,.rel-time.is-live .rel-dot,.sync-btn.is-spin .sync-arrows,.ok-field.is-ok .ok-check path,.unread-row.is-read .unread-check path,.mic-btn.is-on::before,.mic-btn.is-on::after,.ghost-wrap.is-flash,.cmd-palette li.is-run,.flag-row.is-warn,.mention.is-flash b{animation:none!important}

  .grow-link::after,.wipe,.wipe .b,.shuffle .card,.odo-digit > b,.flap-reel,.step-node,.step-line > i,
  .switch,.switch::after,.copy-btn .c-idle,.copy-btn .c-done,.field label,.tip-bubble,.chip,.like-btn svg,
  .disc-btn svg,.disc-panel,.snack,.save-btn,.ux-box,.seg-pill,.soft-tabs-ink,.list-actions,.success-banner,.search-clear,.pin-btn svg,.submit-ring rect,
  .hold-btn .hold-fill,.toast,.menu-btn .menu-line,.stars button,.conn,.retry-btn,.sort-item,.mute-btn .wave,.mute-btn .x-line,.wizard-dots span,.cart-badge,.range-bubble,
  .filter-list li,.upload-bar > i,.quota-track > i,.quota-tip,.splitbtn-toggle svg,.splitbtn-menu,.presence-dot,
  .draft-banner,.tag-chip,.empty-state,.empty-item,.deadline,.deadline-clock,.deadline-track > i,.edge-fade-mask,.dirty-bar,.seen-ticks path,.nudge-field,.stack-card,
  .blur-line,.xface span,.magnet-chip,.confirm-btn,.confirm-btn span,.offline-banner,.sort-flip-btn svg,.sort-flip-list li,.react-fan,.react-fan button,.sticky-cta,
  .pw-toggle .pw-eye,.pw-toggle .pw-slash,.otp input,.exp-search,.exp-search input,.ok-field input,.ok-field .ok-check,.unread-dot,.unread-check,.unread-row,.sync-label,.sync-btn .sync-arrows,.sync-btn .sync-check,
  .inline-edit .ie-title,.inline-edit .ie-rename,.inline-edit .ie-panel,.inline-edit .ie-input,.inline-edit .ie-bar,
  .ghost-wrap .ghost-hint,.ghost-wrap .ghost-key,.cmd-palette,.cmd-palette li,.cmd-stage::before,.crumb-mid,.crumb-more,.diff-add,.diff-add > .diff-add-inner,.slot > i,.zoom-thumb,.zoom-full,.zoom-caption,
  .bulk-bar,.bulk-check svg,.bulk-row,.env-switch .env-ink,.env-switch button,.invite-btn .invite-idle,.invite-btn .invite-done,.flag-row,.flag-sw,.flag-sw::after,.deploy-node,.deploy-node i,.deploy-wire > b,.ws-ink,.ws-item .ws-check,.thread,.thread-body,.thread-resolve svg,
  .unfurl-card,.unfurl-thumb,.seat,.form-prog-bar > i,.form-prog-field,.form-prog-field svg,.mention b,.glyph-tile path,.glyph-tile line,.glyph-tile circle{transition:none!important}

  .draft-banner.is-on{opacity:1;transform:none}

  .diff-pane.is-on .diff-add{grid-template-rows:1fr}

  .diff-pane.is-on .diff-add > .diff-add-inner{opacity:1;transform:none;padding:4px 10px}

  .bulk-row.is-on .bulk-check svg{opacity:1;transform:scale(1)}

  .flag-sw[aria-checked="true"]::after,
  .flag-row.is-on .flag-sw::after{transform:translateX(18px)}

  .ws-item.is-on .ws-check{opacity:1;transform:scale(1)}

  .unfurl.is-on .unfurl-card{grid-template-rows:1fr;opacity:1}

  .unfurl.is-on .unfurl-thumb{opacity:1;transform:none}

  .seat.is-on{transform:none}

  .form-prog-field.is-on svg{opacity:1;transform:scale(1)}
}
```

## JavaScript

```js
// Seat fill
  const seats = document.getElementById('seats');
  const seatLabel = document.getElementById('seat-label');
  const seatLetters = ['A', 'M', 'N', 'S'];
  function syncSeats() {
    if (!seats) return;
    const on = seats.querySelectorAll('.seat.is-on').length;
    if (seatLabel) seatLabel.textContent = on + ' of 4';
  }
  function resetSeats() {
    if (!seats) return;
    seats.querySelectorAll('.seat').forEach((s, i) => {
      s.classList.toggle('is-on', i === 0);
      s.textContent = i === 0 ? 'A' : '+';
    });
    syncSeats();
  }
  function addSeat() {
    if (!seats) return;
    const next = seats.querySelector('.seat:not(.is-on)');
    if (!next) {
      resetSeats();
      return;
    }
    const i = Number(next.getAttribute('data-seat'));
    next.textContent = seatLetters[i] || 'U';
    next.classList.add('is-on');
    syncSeats();
  }

document.querySelectorAll('[data-act]').forEach((btn) => {
    btn.addEventListener('click', (e) => {
      e.stopPropagation();
      const act = btn.getAttribute('data-act');
      if (act === 'seats') addSeat();
    });
  });
```

---

_Source: https://mighil.com/animations/seat-fill_