2nd/10_Wiki/Topics/AI_and_ML/CSS Animations.md

id, title, category, status, canonical_id, aliases, duplicate_of, source_trust_level, confidence_score, verification_status, tags, raw_sources, last_reinforced, github_commit, tech_stack

id	title	category	status	canonical_id	aliases	duplicate_of	source_trust_level	confidence_score	verification_status	tags	raw_sources	last_reinforced	github_commit	tech_stack
wiki-2026-0508-css-animations	CSS Animations & Performance	10_Wiki/Topics	verified	self	CSS animation transform will-change prefers-reduced-motion micro-interaction FLIP animation performance view transitions	none	A	0.93	applied	css animation performance frontend ux accessibility transform will-change prefers-reduced-motion view-transitions		2026-05-10	pending	language framework CSS / JS Web Animations API / Framer Motion / GSAP

CSS Animations

📌 한 줄 통찰

"매 60 FPS 의 transform + opacity". 매 layout property 의 animate = 매 jank. 매 GPU compositor layer 의 ride. 매 modern: 매 prefers-reduced-motion + 매 View Transitions API. 매 functional > decorative.

📖 핵심

매 rendering pipeline

1. Style → 매 CSS apply.
2. Layout (Reflow) → 매 width / height / position 변경.
3. Paint (Repaint) → 매 color / shadow.
4. Composite → 매 GPU layer.

→ 매 transform + opacity 만 의 composite (skip layout, paint).

매 cheap properties (60 FPS)

• ✅ transform: translate, scale, rotate.
• ✅ opacity.
• ✅ filter (some).

매 expensive

• ❌ width, height, padding, margin.
• ❌ top, left (use translate instead).
• ❌ box-shadow, border-radius (some).
• ❌ background image animation.

매 핵심 technique

transform: translate3d(0,0,0) / translateZ(0)

• 매 GPU compositor layer 의 force.
• 매 will-change 의 modern alternative.

will-change: transform

• 매 hint 의 browser optimize.
• 매 overuse 의 memory waste.
• 매 use sparingly.

position: absolute / fixed

• 매 reflow 의 isolate.
• 매 sibling 의 영향 X.

CSS containment

contain: layout paint;  /* 매 reflow 의 contain */

prefers-reduced-motion

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

매 modern primitive

View Transitions API (Chrome 111+)

• 매 same / cross-document transition.
• 매 SPA 의 native.
• 매 baseline 2025 시작.

CSS @starting-style

• 매 entering element 의 initial state.

Scroll-driven animation

• 매 animation-timeline: scroll().
• 매 timeline 의 expand.

CSS @scope

• 매 scoped animation.

매 timing 의 best practice

• Duration: 200-500 ms (UI). 매 너무 길 → 매 wait. 매 너무 짧 → 매 invisible.
• Easing: ease-out (UI 의 보통), ease-in-out (smooth), cubic-bezier (custom).
• Linear: 매 mechanical (loading, progress).

매 functional purpose

1. Feedback: 매 click → 매 visual response.
2. Continuity: 매 state change 의 explain.
3. Hierarchy: 매 importance 의 emphasize.
4. Spatial relation: 매 from / to.
5. Brand personality.

매 anti-purpose

• 매 decoration only.
• 매 attention-seeking infinite loop.
• 매 long entrance animation.
• 매 intrusive auto-play.

매 accessibility

• 매 prefers-reduced-motion: 매 vestibular disorder.
• 매 aria-busy: 매 loading state.
• 매 focus-visible 의 keep.

매 animation library

• Web Animations API (native, modern).
• Framer Motion (React).
• GSAP (general, professional).
• Motion One (lightweight).
• Lottie (designer-friendly).
• Auto-Animate (FLIP automation).

💻 패턴

Cheap animation (transform + opacity)

.button {
  transition: transform 200ms ease-out, opacity 200ms ease-out;
}
.button:hover {
  transform: translateY(-2px) scale(1.02);
  opacity: 0.9;
}

Avoid layout property

/* ❌ Bad — 매 reflow */
.bad {
  transition: left 300ms;
}
.bad:hover { left: 100px; }

/* ✅ Good — 매 composite only */
.good {
  transition: transform 300ms;
}
.good:hover { transform: translateX(100px); }

Reduced motion (accessibility)

.fancy-animation {
  animation: bounce 2s ease infinite;
}

@media (prefers-reduced-motion: reduce) {
  .fancy-animation {
    animation: none;
  }
  
  /* 매 essential 의 keep, fancy 만 의 remove */
  * {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}

View Transitions API

/* Browser-side */
@view-transition {
  navigation: auto;  /* 매 same-document SPA */
}

::view-transition-old(root),
::view-transition-new(root) {
  animation-duration: 250ms;
}

// 매 imperative
async function navigate() {
  if (!document.startViewTransition) {
    updateDOM();
    return;
  }
  document.startViewTransition(() => updateDOM());
}

Scroll-driven animation

@keyframes fade-in {
  from { opacity: 0; transform: translateY(20px); }
  to   { opacity: 1; transform: translateY(0); }
}

.section {
  animation: fade-in 1s linear;
  animation-timeline: view();
  animation-range: entry 0% cover 30%;
}

Web Animations API (JS)

const card = document.querySelector('.card');

const anim = card.animate(
  [{ transform: 'translateY(20px)', opacity: 0 },
   { transform: 'translateY(0)', opacity: 1 }],
  { duration: 300, easing: 'ease-out', fill: 'forwards' },
);

await anim.finished;

FLIP technique (smooth list reorder)

function flipReorder(items, mutate) {
  // 1. First — measure
  const first = new Map();
  items.forEach(el => first.set(el, el.getBoundingClientRect()));
  
  // 2. Last — apply mutation
  mutate();
  
  // 3. Invert + Play
  items.forEach(el => {
    const last = el.getBoundingClientRect();
    const dx = first.get(el).left - last.left;
    const dy = first.get(el).top - last.top;
    
    el.animate(
      [{ transform: `translate(${dx}px, ${dy}px)` }, { transform: 'none' }],
      { duration: 300, easing: 'cubic-bezier(0.2, 0, 0.2, 1)' },
    );
  });
}

Performance: pause off-screen

.spinner { animation: spin 2s linear infinite; }
.spinner.paused { animation-play-state: paused; }

const observer = new IntersectionObserver(entries => {
  entries.forEach(entry => {
    entry.target.classList.toggle('paused', !entry.isIntersecting);
  });
});
document.querySelectorAll('.spinner').forEach(el => observer.observe(el));

Framer Motion (React)

import { motion, AnimatePresence } from 'framer-motion';

<AnimatePresence>
  {isOpen && (
    <motion.div
      initial={{ opacity: 0, y: 20 }}
      animate={{ opacity: 1, y: 0 }}
      exit={{ opacity: 0, y: -20 }}
      transition={{ duration: 0.2, ease: 'easeOut' }}
    >
      Content
    </motion.div>
  )}
</AnimatePresence>

Performance debugging (Chrome DevTools)

1. Chrome DevTools → Performance tab → Record.
2. Look for:
   - Long tasks (>50ms)
   - Layout shift count
   - Paint flashing (Rendering tab)
   - FPS drop
3. Layer borders enable: Rendering → Layer borders.

🤔 결정 기준

상황	Approach
Hover effect	CSS transition (transform, opacity)
Modal entrance	CSS animation + scale + opacity
Page transition (SPA)	View Transitions API
List reorder	FLIP technique
Scroll animation	scroll-driven (modern) or IO + class
Designer-driven	Lottie (designer-friendly)
Complex sequence	GSAP / Framer Motion
Loading	CSS animation + accessibility

기본값: CSS transition + transform + opacity. 매 prefers-reduced-motion. 매 functional only.

🔗 Graph

• 부모: CSS · Web-Performance · Frontend
• 변형: Transform · Opacity · Will-Change · View-Transitions · Scroll-Driven-Animation
• 응용: Web-Animations-API · Framer-Motion · GSAP · Lottie
• Adjacent: Reflow-Repaint · GPU-Acceleration · Accessibility · Baseline-Project

🤖 LLM 활용

언제: 매 frontend animation. 매 micro-interaction. 매 UX polish. 매 accessibility audit. 언제 X: 매 server-side. 매 non-visual.

❌ 안티패턴

• top / left animate: 매 reflow.
• width / height animate: 매 reflow.
• No prefers-reduced-motion: 매 accessibility violation.
• will-change overuse: 매 memory waste.
• Long entrance (>1 sec): 매 user wait.
• Auto-play heavy animation: 매 mobile data + battery.
• Off-screen infinite loop: 매 CPU 의 burn.

🧪 검증 / 중복

• Verified (web.dev animation, MDN, Paul Lewis 의 Aerotwist).
• 신뢰도 A.
• Related: Web-Performance · Accessibility · Baseline-Project · FLIP-Technique.

🕓 Changelog

날짜	변경
2026-04-26	Auto-mapped
2026-05-08	Phase 1
2026-05-10	Manual cleanup — pipeline + cheap/expensive + view-transitions + 매 CSS / FLIP / Framer code