Animation Motion

UI Animation & Motion — Emil Kowalski Design Philosophy

Overview

Taste is trained, not innate. Animation excellence compounds through study and practice—most users never consciously notice individual polish, yet the collection creates stunning results. Beauty is leverage: aesthetic excellence is competitive advantage. This skill applies Emil Kowalski's battle-tested animation decision framework to ship production-grade motion.

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When to Use This Skill

Use when:

• Designing animations for UI components (buttons, modals, dropdowns, popovers, tooltips)
• Reviewing animation implementations for performance and accessibility
• Deciding whether/how/how-fast to animate interactions
• Building gesture-driven interfaces (drag, swipe, hold)
• Optimizing motion for accessibility (prefers-reduced-motion)
• Creating staggered or spring-based animations
• Debugging animation timing, easing, or transform issues

Do NOT use for:

• Animation frameworks/libraries selection (use dedicated framework skills)
• Keyframe animation software (Figma, After Effects)
• SVG animation exclusively (this covers CSS/WAAPI)

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The Animation Decision Framework

Question 1: Should This Animate at All?

Frequency is the primary gate:

| Frequency | Example | Decision | |-----------|---------|----------| | 100+ times/day | Keyboard shortcuts, frequently toggled UI | ❌ Never animate | | Tens of times/day | Hover effects, toggle states | ⚠️ Remove or drastically reduce | | Occasional (few per session) | Modals, toasts, notifications | ✅ Standard animation acceptable | | Rare | Onboarding, celebrations, first-run | ✅ Can add delight | | Keyboard-initiated | Any action from keyboard (return, space, etc.) | ❌ Never animate |

Golden rule: If users interact with it frequently, every millisecond of animation compounds into frustration.

Question 2: What Is the Purpose?

Valid animation purposes:

1. Spatial consistency — clarify origin/destination (modal from center, popover from trigger)
2. State indication — show what changed (button pressed, checkbox checked)
3. Explanation — guide attention or teach (scroll hint, tooltip entrance)
4. Feedback — confirm action received (keystroke feedback, form validation)
5. Preventing jarring changes — smooth transitions between states

Invalid reasons:

• "Looks cool" (unless rare, intentional delight)
• Eye candy for frequently-used UI (animation debt)
• Mimicking competitors without purpose

Question 3: What Easing Curve Should It Use?

Default easing selection:

| Scenario | Easing | Rationale | |----------|--------|-----------| | Element entering/exiting | ease-out | Fast start = responsive; slows to natural stop | | Moving/morphing on screen | ease-in-out | Symmetric motion feels balanced | | Hover/color change | ease | General purpose, smooth | | Constant motion | linear | Clock-like consistency |

CRITICAL: Use custom easing curves, not CSS defaults:

:root {
  --ease-out: cubic-bezier(0.23, 1, 0.32, 1);
  --ease-in-out: cubic-bezier(0.77, 0, 0.175, 1);
  --ease-drawer: cubic-bezier(0.32, 0.72, 0, 1);
}

Never use ease-in for UI animations — delays initial movement, feels sluggish and unresponsive.

Question 4: How Fast Should It Be?

Duration guidelines:

| Component | Duration Range | Rationale | |-----------|-----------------|-----------| | Button press feedback | 100–160ms | Instant perceived feedback | | Tooltips/small popovers | 125–200ms | Quick appearance | | Dropdowns/selects | 150–250ms | Slightly longer for scope change | | Modals/drawers | 200–500ms | Larger movement space | | Marketing/explanatory | Flexible | Can extend for teaching |

Rule of thumb: UI animations under 300ms. Anything longer feels like loading.

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Spring Animations — Alive Motion

Springs simulate physics naturally. Duration emerges from physics parameters, not fixed time. Use for:

• Drag interactions (user expects momentum)
• "Alive" elements that feel responsive
• Interruptible gestures (springs maintain velocity when interrupted)
• Decorative mouse-tracking effects

Apple-style config:

{
  type: "spring",
  duration: 0.5,
  bounce: 0.2  // 0.1-0.3 recommended; keep subtle
}

Traditional config (Framer Motion):

{
  type: "spring",
  mass: 1,
  stiffness: 100,
  damping: 10
}

Key insight: Springs maintain velocity when interrupted. CSS animations restart from zero (rigid).

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Component Animation Patterns

Buttons

/* Base */
button {
  transition: transform 160ms var(--ease-out);
}

/* Active state — subtle press feedback */
button:active {
  transform: scale(0.97);
}

Why 0.97, not 0.95? Subtle feedback feels refined; aggressive scale looks cheap.

Never Animate From scale(0)

/* ❌ BAD — jarring entrance, feels cheap */
@keyframes popIn {
  from { transform: scale(0); }
  to { transform: scale(1); }
}

/* ✅ GOOD — smooth, natural entrance */
@keyframes popIn {
  from { transform: scale(0.95); opacity: 0; }
  to { transform: scale(1); opacity: 1; }
}

Popovers — Origin-Aware

/* Popover respects where it originated from */
[data-radix-popover-content] {
  transform-origin: var(--radix-popover-content-transform-origin);
  animation: popoverEnter 200ms var(--ease-out);
}

@keyframes popoverEnter {
  from {
    opacity: 0;
    transform: scale(0.95);
  }
  to {
    opacity: 1;
    transform: scale(1);
  }
}

Modals keep center origin — always transform-origin: center center.

Tooltips — Smart Delays

/* First appearance: delay to confirm intent */
[role="tooltip"] {
  transition: opacity 200ms var(--ease-out);
  transition-delay: 300ms;
}

/* Subsequent hovers: instant (user already hovering element) */
[role="tooltip"][data-instant] {
  transition-delay: 0ms;
}

CSS Transitions vs. Keyframes

• Use CSS transitions for interruptible UI (user can stop mid-animation)
• Use keyframes for deterministic, looping effects (loading spinners, constant motion)
• Transitions are superior for most UI because they handle interruption gracefully.

Blur for Masking Imperfect Transitions

/* During fade transitions, slight blur hides interpolation artifacts */
[data-transitioning] {
  filter: blur(2px);
  transition: filter 200ms var(--ease-out);
}

[data-transitioning][data-done] {
  filter: blur(0px);
}

Keep blur under 20px; large blur reads as visual glitch.

@starting-style for Entry Animations (CSS-only)

/* Define "before" state without JavaScript */
dialog {
  opacity: 1;
  translate: 0 0;
  animation: dialogEnter 300ms var(--ease-out);
}

@starting-style {
  dialog {
    opacity: 0;
    translate: 0 -20px;
  }
}

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CSS Transform Mastery

translateY with Percentages

/* Percentage relative to ELEMENT SIZE, not viewport */
[data-drawer] {
  transform: translateY(100%);  /* Moves down by element's own height */
  transition: transform 300ms var(--ease-drawer);
}

[data-drawer][data-open] {
  transform: translateY(0);
}

scale() Propagates to Children

/* Parent scale affects children proportionally */
.parent {
  transform: scale(0.95);  /* All descendants scale 0.95x */
}

3D Transforms with Preserve-3D

.card {
  transform-style: preserve-3d;
  transform: rotateX(15deg) rotateY(-10deg);
}

.card-face {
  transform: translateZ(20px);  /* Lifts face forward in 3D space */
}

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clip-path for Advanced Animation

Use for rectangular masks:

/* Reveal from top down */
.reveal {
  clip-path: inset(0 0 100% 0);
  animation: revealDown 400ms var(--ease-out) forwards;
}

@keyframes revealDown {
  to { clip-path: inset(0 0 0 0); }
}

Use cases:

• Tab color transitions (reveal new color under existing)
• Hold-to-delete progress indicators
• Image reveals on scroll
• Comparison sliders (before/after)

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Gesture and Drag Interactions

Momentum-Based Dismissal

// User swipes dismissible element
element.addEventListener('pointerup', (event) => {
  const velocity = calculateVelocity(event);

  if (Math.abs(velocity) > DISMISS_THRESHOLD) {
    // Use spring to carry momentum
    element.animate([
      { transform: 'translateY(0)' },
      { transform: 'translateY(100%)' }
    ], {
      duration: 300,
      easing: 'cubic-bezier(0.32, 0.72, 0, 1)'
    });
  }
});

Boundary Friction (Not Hard Stops)

// Damping at boundaries instead of walls
let velocity = getVelocity();
if (element.y > MAX_Y) {
  velocity *= 0.95;  // Friction dampens momentum
}

setPointerCapture() for Cross-Document Tracking

element.addEventListener('pointerdown', (event) => {
  element.setPointerCapture(event.pointerId);
  // All subsequent pointer events target this element, even off-screen
});

element.addEventListener('pointermove', (event) => {
  if (event.isPrimary) {
    // Only respond to primary pointer (not secondary touch)
    updateDrag(event.clientX, event.clientY);
  }
});

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Performance Rules

Only Animate transform and opacity

/* ✅ GOOD — GPU accelerated, no repaints */
.button {
  transition: transform 160ms var(--ease-out), opacity 160ms var(--ease-out);
}

/* ❌ BAD — triggers reflow on every frame */
.button {
  transition: width 160ms, height 160ms, padding 160ms;
}

CSS Variables for Coordinated Animations

:root {
  --animation-duration: 300ms;
  --animation-easing: var(--ease-out);
}

.modal {
  animation: modalEnter var(--animation-duration) var(--animation-easing);
}

.modal-overlay {
  animation: overlayFade var(--animation-duration) var(--animation-easing);
}

CSS Animations Beat JavaScript Under Load

• Use CSS transitions/animations for UI
• Use JavaScript (Web Animation API) for complex, programmatic effects
• Profile on real devices (mobile especially)

WAAPI (Web Animation API) for Programmatic CSS

element.animate([
  { transform: 'translateY(-100px)', opacity: 0 },
  { transform: 'translateY(0)', opacity: 1 }
], {
  duration: 300,
  easing: 'cubic-bezier(0.23, 1, 0.32, 1)',
  fill: 'forwards'
});

Verify on real devices, always. Desktop Chrome may hide jank that's visible on iPhone.

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Accessibility — Non-Negotiable

Always Respect prefers-reduced-motion

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
  }
}

Not optional. Users with vestibular disorders experience nausea from motion.

Use @media (hover: hover) for Hover-Only Effects

/* Only show hover effects on devices that support hover */
@media (hover: hover) {
  button:hover {
    opacity: 0.8;
  }
}

Prevents ghost states on touch devices.

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Stagger Animations — Visual Rhythm

Animate multiple elements in sequence, not simultaneously:

.item {
  opacity: 0;
  animation: itemEnter 300ms var(--ease-out) forwards;
}

.item:nth-child(1) { animation-delay: 0ms; }
.item:nth-child(2) { animation-delay: 50ms; }
.item:nth-child(3) { animation-delay: 100ms; }

Effect: Creates visual rhythm, guides attention, feels intentional.

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Sonner Principles — Polish Compounding

1. Cohesion: Every detail works together. No random animations.
2. Opacity + Height: Sophisticated reveals use combined opacity and height shifts, not just fade.
3. Fresh eyes review: Review animations the next day. What felt good at 3 AM looks different at noon.
4. Asymmetric enter/exit timing: Fast entrance (100-150ms), slower exit (200-300ms). Feels snappier.

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Debugging Animations

Slow Motion Testing in DevTools

1. Open DevTools (F12)
2. Animations panel → Slow down playback (10x)
3. Frame-by-frame inspection reveals micro-timing issues

Debug Checklist

• Does animation respond immediately to user input?
• Does easing curve feel natural (not robotic)?
• Does animation maintain 60fps on mobile? (DevTools Performance tab)
• Is motion purpose clear (spatial, feedback, state)?

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Quick Reference Table

| Aspect | Rule | |--------|------| | Button press | 100-160ms, scale(0.97), ease-out | | Modal entrance | 200-500ms, origin-aware, ease-out | | Dropdown open | 150-250ms, ease-out | | Hover state | Remove or keep 10x/day; animation removed | | Modal scale(0) entrance | Modal scale(0.95) entrance | Smoother, less jarring visual | | 500ms dropdown open | 200ms dropdown open | Felt laggy; 200ms is perceptually instant |

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Common Mistakes

1. Animating Frequently-Used Interactions

// ❌ BAD — submitted 100x/day, animation compounds to ~3 min/day lost
buttonSubmit.addEventListener('click', () => {
  showLoadingSpinner();  // 300ms animation
});

// ✅ GOOD — instant feedback, no animation
buttonSubmit.disabled = true;
buttonSubmit.textContent = 'Loading...';

2. Using ease-in for UI

/* ❌ BAD — delays initial movement, feels unresponsive */
.modal {
  transition: opacity 300ms ease-in;
}

/* ✅ GOOD — fast start, natural deceleration */
.modal {
  transition: opacity 300ms cubic-bezier(0.23, 1, 0.32, 1);
}

3. Hardcoded Timing (No Coordination)

/* ❌ BAD — impossible to adjust globally */
.modal { animation: modalEnter 350ms ease-out; }
.overlay { animation: overlayFade 300ms ease-out; }
.button { animation: buttonSlide 250ms ease-out; }

/* ✅ GOOD — adjust once, applies everywhere */
:root {
  --duration-modal: 300ms;
  --duration-feedback: 150ms;
}

.modal { animation: modalEnter var(--duration-modal) var(--ease-out); }

4. Forgetting prefers-reduced-motion

/* ❌ BAD — ignores accessibility preference */
.animation { animation: spin 1s linear infinite; }

/* ✅ GOOD — respects user preference */
.animation { animation: spin 1s linear infinite; }
@media (prefers-reduced-motion: reduce) {
  .animation { animation: none; }
}

5. Scale From Zero

// ❌ BAD
element.style.transform = 'scale(0)';
setTimeout(() => {
  element.style.transform = 'scale(1)';
}, 0);

// ✅ GOOD
element.style.transform = 'scale(0.95)';
element.style.opacity = '0';
setTimeout(() => {
  element.style.transform = 'scale(1)';
  element.style.opacity = '1';
}, 0);

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Final Principle

Taste is trained. Study animations in Apple Mail, Linear, Stripe, Arc Browser. Screenshot the good ones. Copy the feeling (not the code). Practice writing micro-interactions. Review with fresh eyes. Ship, measure, iterate.

Every 100ms compounded across millions of interactions shapes user perception. Excellence is leverage.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: fernando-bertholdo
• Source: fernando-bertholdo/4-successful-AI-life
• License: MIT

Install and usage instructions live in the source repository linked above.