Motion

Motion explains change and confirms input. If it does neither, it is decoration and needs a reason.

1. Should it animate?

Never animate keyboard-triggered actions.

2. Easing

• Entering or exiting: strong ease-out cubic-bezier(.23, 1, .32, 1).
• Moving on screen: ease-in-out cubic-bezier(.77, 0, .175, 1).
• Drawers/sheets: cubic-bezier(.32, .72, 0, 1).
• Colour/hover: ease. Constant motion (marquee, progress): linear.
• Never ease-in for UI; it feels laggy at the moment the user is watching.

3. Duration

Press 100-160ms · tooltip 125-200ms · dropdown 150-250ms · modal/drawer 200-400ms · marketing hero up to 800ms. Exits ~20% faster than entrances. UI motion stays under 300ms.

4. Craft rules

• Animate transform and opacity only. Never width, height, top, left, or transition: all.
• Nothing appears from scale(0); start at scale(.95) + opacity: 0.
• Popovers and menus scale from their trigger (transform-origin at the trigger). Modals stay centred.
• Buttons: :active { transform: scale(.97) } with a 120ms transition.
• Tooltips: delay the first one (~400ms); adjacent ones open instantly.
• Stagger lists by 30-50ms per item, cap the total under 400ms.
• Scroll reveals: one per page at most, small distance (8-16px), run once. Not on every section.
• Springs (Motion/Framer, React Spring) for drag, gestures and interruptible movement: { type: "spring", duration: .4, bounce: .15 }. Keep bounce at 0.1-0.3, and only on playful surfaces.
• Prefer CSS transitions and @starting-style for simple enter/exit; the View Transitions API for page/state morphs; a JS library only when gestures or sequences need it.

5. Reduced motion (required)

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: .01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: .01ms !important;
    scroll-behavior: auto !important;
  }
}

Keep opacity changes and state colour; remove movement, parallax and shake.

Review format

When reviewing motion code, answer with a table: | Before | After | Why |, one row per issue.