AI-consumed reference. Taste + technique for motion; the perf ceiling is owned by rules/agent/frontend-excellence.md — cross-reference its budget, don't restate it.

Motion Design

Motion should clarify, not decorate. Small, fast, purposeful. House style: subtle — no bouncy/springy overshoot as decoration, no infinite loops competing for attention.

prefers-reduced-motion is MANDATORY

Every motion example MUST honor it — non-negotiable. Wrap transitions so reduced-motion collapses them to an instant (opacity-only or none):

@media (prefers-reduced-motion: reduce) { *, ::before, ::after { animation: none !important; transition: none !important; } }

In Framer Motion, gate variants on useReducedMotion() and drop transforms.

Two tools, matched to impact

• CSS-only for reveals/stagger (cheapest, no JS): stagger via animation-delay: calc(var(--i) * 60ms) on a keyframed fade-up. Use for hero/list entrance where you don't need interaction.
• Framer Motion for stateful/interactive motion: declarative variants + initial/animate, shared layout, gesture. Prefer it only where CSS can't express the state.

Bundle discipline

Framer Motion is heavy — use LazyMotion + m. components (load domAnimation features on demand) instead of the full motion. import. This keeps it within the frontend-excellence perf budget.