UI Animation

Core rules

• Animate to clarify cause/effect or add deliberate delight.
• Keep interactions fast (200-300ms; up to 1s only for illustrative motion).
• Never animate keyboard interactions (arrow-key navigation, shortcut responses, tab/focus).
• Prefer CSS; use WAAPI or JS only when needed.
• Make animations interruptible and input-driven.
• Honor prefers-reduced-motion (reduce or disable).

What to animate

• For movement and spatial change, animate only transform and opacity.
• For simple state feedback, color, background-color, and opacity transitions are acceptable.
• Never animate layout properties; never use transition: all.
• Avoid filter animation for core interactions; if unavoidable, keep blur <= 20px.
• SVG: apply transforms on a <g> wrapper with transform-box: fill-box; transform-origin: center.
• Disable transitions during theme switches.

Spatial and sequencing

• Set transform-origin at the trigger point.
• For dialogs/menus, start around scale(0.85-0.9); avoid scale(0).
• Stagger reveals <= 50ms.

Easing defaults

• Enter and transform-based hover: cubic-bezier(0.22, 1, 0.36, 1).
• Move: cubic-bezier(0.25, 1, 0.5, 1).
• Simple hover colour/background/opacity: 200ms ease.
• Avoid ease-in for UI (feels slow).

Accessibility

• If transform is used, disable it in prefers-reduced-motion.
• Disable hover transitions on touch devices via @media (hover: hover) and (pointer: fine).

Performance

• Pause looping animations off-screen.
• Toggle will-change only during heavy motion and only for transform/opacity.
• Prefer transform over positional props in animation libraries.
• Do not animate drag gestures using CSS variables.

Reference

• Snippets and practical tips: examples.md

Workflow

1. Start with the core rules, then pick a reference snippet from examples.md.
2. Keep motion functional; honor prefers-reduced-motion.
3. When reviewing, cite file paths and line numbers and propose concrete fixes.
4. Validate:
   • Test with prefers-reduced-motion: reduce enabled — animations must degrade gracefully.
   • Verify no layout property animations (width, height, top, left).
   • Check that looping animations pause off-screen.
   • Confirm will-change is toggled only during animation, not permanently set.