# Diff insert

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

- **Live demo:** https://mighil.com/animations/diff-insert
- **Standalone HTML:** https://mighil.com/animations/diff-insert?download=1
- **This file:** https://mighil.com/animations/diff-insert/diff-insert.md
- **Technique:** `change`

## What it does

New line grows into the diff instead of just flashing green.

## 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="diff-pane" id="diff-pane" aria-label="Code diff">
        <div class="diff-line"><span class="n">14</span><span>function ship() {'{'}</span></div>
        <div class="diff-add"><div class="diff-add-inner"><span class="n">15</span><span class="mark">+</span><span>  await notify();</span></div></div>
        <div class="diff-line"><span class="n">16</span><span>{'}'}</span></div>
      </div>
```

## CSS

```css
.diff-pane{
  width:min(100%,340px);border-radius:8px;overflow:hidden;font-family:ui-monospace,SFMono-Regular,Menlo,Consolas,monospace;
  border:1px solid color-mix(in srgb,var(--text-color) 12%,transparent);font-size:.78rem;line-height:1.55;
}

.diff-line{display:flex;gap:10px;padding:4px 10px;color:color-mix(in srgb,var(--text-color) 70%,transparent)}

.diff-line .n{width:1.2em;opacity:.4;text-align:right;flex-shrink:0}

.diff-add{
  display:grid;grid-template-rows:0fr;
  background:color-mix(in srgb,#2a8 10%,transparent);
  color:inherit;
  transition:grid-template-rows .45s cubic-bezier(.22,1,.36,1);
}

.diff-add > .diff-add-inner{
  overflow:hidden;min-height:0;
  display:flex;gap:10px;padding:0 10px;
  opacity:0;transform:translateY(-4px);
  transition:opacity .3s ease .08s,transform .35s cubic-bezier(.22,1,.36,1) .05s,padding .35s ease;
}

.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;
}

.diff-add .mark{color:color-mix(in srgb,#2a8 70%,var(--text-color));width:1em;flex-shrink:0}

@media (prefers-reduced-motion: reduce){
  .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}

  .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}
}
```

## JavaScript

```js
// Diff insert
  const diffPane = document.getElementById('diff-pane');
  let diffTimer = null;
  function runDiff() {
    if (!diffPane) return;
    clearTimeout(diffTimer);
    diffPane.classList.remove('is-on');
    void diffPane.offsetWidth;
    if (reduce) {
      diffPane.classList.add('is-on');
      return;
    }
    diffTimer = setTimeout(() => {
      requestAnimationFrame(() => diffPane.classList.add('is-on'));
    }, 120);
  }
  runDiff();

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

---

_Source: https://mighil.com/animations/diff-insert_