---
id: wiki-2026-0508-css-modules
title: CSS Modules
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [CSS Module, Locally-Scoped CSS]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [css, frontend, scoping, build-tool]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: css
  framework: webpack/vite
---

# CSS Modules

## 매 한 줄
> **"매 class 가 file-locally scoped"**. CSS Modules 매 build-time transform 으로 매 class name 을 unique hash 로 rewriting — 매 global namespace pollution 의 elimination + component-level encapsulation 의 enable. 매 2026 현재 Vite/Webpack/Next.js 매 native support, 매 CSS-in-JS runtime cost 의 alternative 로 주류.

## 매 핵심

### 매 작동 원리
- `Button.module.css` 매 import 시 매 bundler 가 매 class 를 `Button_primary__a3fG2` 로 rename.
- 매 import 결과 매 object — `{ primary: 'Button_primary__a3fG2' }`.
- 매 component 매 `styles.primary` 로 reference — 매 collision-free.

### 매 vs alternatives
- **vs global CSS**: 매 scoping 자동, 매 BEM 매 manual convention 의 replacement.
- **vs CSS-in-JS**: 매 zero runtime, 매 build-time only — 매 bundle size + perf 우위.
- **vs Tailwind**: 매 component-local custom design 매 적합, Tailwind 매 utility-first.

### 매 응용
1. Component library (Button, Input) 매 encapsulated styling.
2. Next.js 매 default-supported pattern — `*.module.css` 매 convention.
3. Design system 매 token + component 매 layered structure.

## 💻 패턴

### Basic usage
```css
/* Button.module.css */
.primary {
  background: #0070f3;
  color: white;
  padding: 8px 16px;
  border-radius: 4px;
}

.disabled {
  opacity: 0.5;
  cursor: not-allowed;
}
```

```tsx
// Button.tsx
import styles from './Button.module.css';

export function Button({ disabled, children }: Props) {
  return (
    <button
      className={`${styles.primary} ${disabled ? styles.disabled : ''}`}
      disabled={disabled}
    >
      {children}
    </button>
  );
}
```

### Composition (`composes`)
```css
/* base.module.css */
.button {
  font: inherit;
  cursor: pointer;
}

/* Button.module.css */
.primary {
  composes: button from './base.module.css';
  background: #0070f3;
}
```

### `clsx` 와 conditional classes
```tsx
import clsx from 'clsx';
import styles from './Card.module.css';

export function Card({ variant, active }: Props) {
  return (
    <div className={clsx(styles.card, styles[variant], active && styles.active)}>
      ...
    </div>
  );
}
```

### TypeScript typed module
```ts
// Button.module.css.d.ts (auto-generated by typescript-plugin-css-modules)
declare const styles: {
  readonly primary: string;
  readonly disabled: string;
};
export default styles;
```

### `:global` escape hatch
```css
/* Layout.module.css */
.root :global(.markdown) h1 {
  /* unscoped — for third-party HTML */
  font-size: 2rem;
}
```

### Vite config
```ts
// vite.config.ts
export default {
  css: {
    modules: {
      localsConvention: 'camelCaseOnly',
      generateScopedName: '[name]__[local]__[hash:base64:5]',
    },
  },
};
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| Component-scoped styling, zero runtime | **CSS Modules** |
| Dynamic styles (props-driven) | CSS-in-JS (vanilla-extract, styled-components) |
| Utility-first, rapid prototyping | Tailwind |
| Server Components 매 styling | CSS Modules (Tailwind 도 OK) |

**기본값**: Next.js / Vite 매 component-level styling 의 first choice 로 **CSS Modules**.

## 🔗 Graph
- 변형: [[CSS_Architecture_and_Styling|CSS-in-JS]] · [[CSS_Architecture_and_Styling|Tailwind CSS]] · [[BEM]]
- 응용: [[Next.js]] · [[Vite]] · [[React]]
- Adjacent: [[Vanilla-Extract]]

## 🤖 LLM 활용
**언제**: component encapsulation 매 필요, runtime cost 의 회피, TypeScript-friendly typing.
**언제 X**: 매 dynamic theming 매 heavy (variant explosion), 매 design token 매 runtime mutation 매 필요 — vanilla-extract / CSS variables.

## ❌ 안티패턴
- **`:global` 매 남용**: 매 scoping benefit 의 nullification.
- **String concatenation 매 raw**: 매 `clsx` 의 사용 — 매 readability + falsy handling.
- **`styles['kebab-case']` access 매 unnecessarily**: 매 `localsConvention: 'camelCaseOnly'` 매 설정.
- **Module 1개 매 100+ classes**: 매 split — 매 component-per-module.

## 🧪 검증 / 중복
- Verified (Next.js docs 2026, Vite CSS Modules guide).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — CSS Modules build-time scoping + composition + Vite/Next 통합 |
