---
id: wiki-2026-0508-dynamic-theming
title: Dynamic Theming
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [Theming, Dark Mode, CSS Variables Theming]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [frontend, css, theming, design-system]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: TypeScript
  framework: React
---

# Dynamic Theming

## 매 한 줄
> **"매 design token 을 runtime swap 할 수 있는 architecture"**. CSS custom properties (variables) 가 매 modern theming 의 backbone 이며, JS bundle 의 무관 하게 instant theme switching 의 가능. 2026 의 light/dark/high-contrast/brand-variant 의 매 standard.

## 매 핵심

### 매 3-layer token 구조
- **Primitive tokens**: raw values (`--blue-500: #3B82F6`).
- **Semantic tokens**: intent-based (`--color-primary: var(--blue-500)`).
- **Component tokens**: scope-specific (`--button-bg: var(--color-primary)`).

### 매 swap 메커니즘
- `data-theme="dark"` 속성 의 `<html>` element 의 set.
- CSS 의 `[data-theme="dark"] { --color-bg: #0a0a0a }` 의 override.
- 매 zero JS re-render — 매 paint cycle 만 trigger.

### 매 응용
1. Light/dark mode toggle.
2. Brand white-labeling (multi-tenant SaaS).
3. Accessibility (high-contrast, reduced-motion variant).
4. Per-user customization (saved theme preference).

## 💻 패턴

### Token 정의 (CSS)
```css
:root {
  /* Primitive */
  --blue-500: #3B82F6;
  --gray-900: #111827;
  --gray-50:  #F9FAFB;

  /* Semantic — light default */
  --color-bg: var(--gray-50);
  --color-fg: var(--gray-900);
  --color-primary: var(--blue-500);
}

[data-theme="dark"] {
  --color-bg: var(--gray-900);
  --color-fg: var(--gray-50);
}

[data-theme="high-contrast"] {
  --color-bg: #000;
  --color-fg: #fff;
  --color-primary: #ffff00;
}
```

### Theme provider (React 19)
```tsx
import { createContext, use, useEffect, useState } from "react";

type Theme = "light" | "dark" | "system";
const ThemeCtx = createContext<{ theme: Theme; set: (t: Theme) => void }>(null!);

export function ThemeProvider({ children }: { children: React.ReactNode }) {
  const [theme, setTheme] = useState<Theme>(
    () => (localStorage.getItem("theme") as Theme) ?? "system"
  );

  useEffect(() => {
    const resolved =
      theme === "system"
        ? matchMedia("(prefers-color-scheme: dark)").matches ? "dark" : "light"
        : theme;
    document.documentElement.dataset.theme = resolved;
    localStorage.setItem("theme", theme);
  }, [theme]);

  return <ThemeCtx value={{ theme, set: setTheme }}>{children}</ThemeCtx>;
}

export const useTheme = () => use(ThemeCtx);
```

### FOUC 방지 (inline script)
```html
<!-- <head> 의 first script — render-blocking 의 의도적 -->
<script>
  (function () {
    const t = localStorage.getItem("theme") || "system";
    const resolved = t === "system"
      ? (matchMedia("(prefers-color-scheme: dark)").matches ? "dark" : "light")
      : t;
    document.documentElement.dataset.theme = resolved;
  })();
</script>
```

### Tailwind 4 의 통합
```css
@import "tailwindcss";

@theme {
  --color-bg: var(--bg);
  --color-fg: var(--fg);
}

:root         { --bg: #fff; --fg: #111; }
[data-theme="dark"] { --bg: #0a0a0a; --fg: #f5f5f5; }
```

```tsx
<div className="bg-bg text-fg">매 theme-aware</div>
```

### System preference 의 listen
```ts
const mq = matchMedia("(prefers-color-scheme: dark)");
mq.addEventListener("change", (e) => {
  if (localStorage.getItem("theme") === "system") {
    document.documentElement.dataset.theme = e.matches ? "dark" : "light";
  }
});
```

### View Transitions API (smooth swap)
```ts
function toggleTheme() {
  if (!document.startViewTransition) {
    flipTheme();
    return;
  }
  document.startViewTransition(() => flipTheme());
}
```

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

### Brand variant (multi-tenant)
```css
[data-brand="acme"]   { --color-primary: #FF6B35; }
[data-brand="globex"] { --color-primary: #2EB872; }
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| Static site / blog | CSS variable + `data-theme` |
| SaaS multi-tenant | CSS variable + brand attribute layer |
| RN / Native | Theme context + StyleSheet (no CSS vars) |
| Tailwind 의 사용 | Tailwind 4 `@theme` + CSS variable |
| Email template | Inline styles + `prefers-color-scheme` media query |

**기본값**: CSS custom properties + `data-theme` attribute + inline FOUC script.

## 🔗 Graph
- 부모: [[CSS_Architecture_and_Styling|CSS Architecture]] · [[Design Tokens]]
- 변형: [[Tailwind CSS 4]] · [[CSS_Architecture_and_Styling|CSS-in-JS]]
- 응용: [[Dark Mode]] · [[Accessibility (a11y)]]
- Adjacent: [[View Transitions API]]

## 🤖 LLM 활용
**언제**: design token system 의 설계, dark mode 구현, multi-brand theming.
**언제 X**: simple 의 single-color brand 의 — 매 over-engineering.

## ❌ 안티패턴
- **JS-only theme**: setState 의 모든 component re-render — 매 slow 의.
- **Hard-coded color in component**: token 의 bypass — 매 swap 불가능.
- **No FOUC script**: hydration 전 wrong theme flash — 매 jarring UX.
- **Theme 의 localStorage 의만 의존**: SSR 의 server-render mismatch.

## 🧪 검증 / 중복
- Verified (MDN, web.dev, Tailwind CSS docs, Adobe Spectrum 의 token system).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — 3-layer token + FOUC + View Transitions 추가 |
