---
id: css-optimization
title: "CSS Optimization"
category: "Frontend"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["CSS performance", "CSS optimization", "faster CSS", "CSS minification", "render performance"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.87
created_at: 2026-06-23
updated_at: 2026-06-23
review_reason: ""
merge_history: []
tags: ["css", "web", "frontend", "w3schools", "performance", "optimization", "rendering"]
raw_sources: ["https://www.w3schools.com/css/css_performance.asp"]
applied_in: []
github_commit: ""
---

# [[CSS Optimization]]

## 🎯 한 줄 통찰 (One-line insight)
Optimizing CSS makes a website load faster and run more smoothly — keep selectors simple, avoid layout-thrashing work, animate cheap properties, and serve external, minified, cached stylesheets. [S1]

## 🧠 핵심 개념 (Core concepts)
- **Why optimize** — optimizing CSS makes your website load faster and run more smoothly, which results in a better user experience. [S1]
- **Parsing cost** — complex selectors increase parsing time, so simpler selectors are faster. [S1]
- **Rendering cost** — broad selectors (like the universal selector) and certain animated properties force more work during rendering. [S1]
- **Delivery cost** — how CSS is loaded, combined, minified, and cached affects load time. [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **Simplest-selector pattern** — prefer a short selector such as `.button:hover` over a deeply nested one. [S1]
- **Cheap-animation pattern** — animate properties that don't cause repaint/reflow (transforms, opacity, filter) instead of layout-triggering properties. [S1]
- **One-file delivery pattern** — combine into a single external CSS file, minify it, and cache it with a long expiration time. [S1]

## 📖 세부 내용 (Details)
Optimizing CSS makes your website load faster and run more smoothly, which also results in a better user experience. The page presents nine optimization strategies. [S1]

**1. Use Simple Selectors.** Use simple selectors when possible; complex selectors increase the parsing time. The "bad" approach uses a deeply nested selector, while the better approach uses just `.button:hover`. [S1]

**2. Avoid the Universal Selector.** Avoid the universal selector (`*`) when not strictly necessary — it affects every element and can slow down page rendering. [S1]

**3. Avoid Inline Styles.** Avoid inline styles when not necessary; inline styles make your HTML heavier and are harder to manage. [S1]

**4. Avoid `@import`.** Avoid using `@import` for loading external CSS, as it delays stylesheet loading. Use the `<link>` tag in the `<head>` section instead. [S1]

**5. Use Shorthand Properties.** Use shorthand properties when possible — it saves space and is faster to parse. For example, use `margin: 10px 20px;` instead of writing each margin property individually. [S1]
```css
margin: 10px 20px;
```

**6. Cut Down Unnecessary Animations.** A high number of animations and large animations require more processing power to handle, which degrades performance. [S1]

**7. Use Properties That Don't Cause Repaint.** Animation performance relies also on what properties you are animating. Properties like transforms, opacity, and filter are recommended over layout-triggering properties. [S1]

**8. Combine and Minify CSS.** Use one CSS file when possible, and remove spaces and comments to reduce file size. [S1]

**9. Cache Your CSS.** Make sure your CSS file is cached by the browser by giving it a long expiration time in your server settings. [S1]

**Summary.** Keep selectors short and simple; avoid layout-thrashing operations; use efficient animation techniques; and use external, minified, and cached stylesheets. [S1]

(Note: the exact "bad" vs "good" verbatim code boxes for tips 1–4 and 6–9 were not captured verbatim from the source beyond the shorthand `margin` example and the `.button:hover` reference. — Not found in source.)

## 🛠️ 적용 사례 (Applied in summary)
The page's applied guidance contrasts a deeply nested selector against the simpler `.button:hover`, and replaces individual margin declarations with the shorthand `margin: 10px 20px;`. No external project/commit applications found in the source.

## 💻 코드 패턴 (Code patterns)
Shorthand over longhand (language: CSS):
```css
/* Preferred — shorthand */
margin: 10px 20px;
```
Simple selector over a nested chain (language: CSS):
```css
/* Preferred — short and simple */
.button:hover { /* ... */ }
```

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
No contradictions found in the source.

## ✅ 검증 상태 및 신뢰도
- **상태:** draft
- **검증 단계:** conceptual (실제 적용 사례 발견 시 applied/validated로 승격 가능)
- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
- **신뢰 점수:** 0.87
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[CSS Tutorial]]
- **관련 개념:** [[CSS Selectors]], [[CSS Math Functions]], [[CSS Accessibility]]
- **참조 맥락:** Consulted when a page's CSS is slow to parse, render, or download and needs tuning for performance.

## 📚 출처 (Sources)
- [S1] W3Schools — CSS Optimization — https://www.w3schools.com/css/css_performance.asp

## 📝 변경 이력 (Change history)
- 2026-06-23: Initial draft synthesized from the W3Schools "CSS Optimization" page (Astra wiki-curation, P-Reinforce v3.1 format).
