---
id: css-variables-in-media-queries
title: "CSS Variables in Media Queries"
category: "Frontend"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["CSS custom properties media queries", "responsive CSS variables", "override variable in @media", "--fontsize media query", "variable breakpoints"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.88
created_at: 2026-06-23
updated_at: 2026-06-23
review_reason: ""
merge_history: []
tags: ["css", "web", "frontend", "w3schools", "css-variables", "media-queries", "responsive"]
raw_sources: ["https://www.w3schools.com/css/css3_variables_mediaqueries.asp"]
applied_in: []
github_commit: ""
---

# [[CSS Variables in Media Queries]]

## 🎯 한 줄 통찰 (One-line insight)
CSS variables can be reassigned inside `@media` rules, so a single `var()`-driven design responds to screen size simply by overriding the variable's value at a breakpoint. [S1]

## 🧠 핵심 개념 (Core concepts)
- **Media queries enable responsive styling** — they allow you to set different styles for different devices/screen sizes. [S1]
- **Variables are overridable per breakpoint** — you can change a variable's value inside a media query, and every rule that reads it via `var()` updates automatically. [S1]
- **Local vs. root scope** — a variable defined on `.container` (e.g. `--fontsize`) can be overridden for `.container` inside a media query, while a variable on `:root` (e.g. `--primary-bg-color`) can be overridden globally inside the same query. [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **Breakpoint override pattern** — redefine the variable inside `@media screen and (min-width: …)` to switch its value above that width. [S1]
- **Single-property responsiveness** — changing `--fontsize` from `20px` to `40px` at `min-width: 450px` makes the font-size responsive without touching the `font-size` declaration itself. [S1]
- **Multi-variable override** — multiple variables (a local `--fontsize` on `.container` and a global `--primary-bg-color` on `:root`) can be overridden together within one media query. [S1]

## 📖 세부 내용 (Details)
Media queries let you set different style values for different devices. The page demonstrates overriding a CSS variable's value based on screen width: the `--fontsize` variable is `20px` on small screens and becomes `40px` on screens that are `450px` or wider. [S1]

**Example 1 — override a single variable at a breakpoint** [S1]
```css
:root {
  --primary-bg-color: #1e90ff;
  --primary-color: #ffffff;
}

body {
  background-color: var(--primary-bg-color);
}

.container {
  --fontsize: 20px;
  color: var(--primary-bg-color);
  background-color: var(--primary-color);
  padding: 15px;
  font-size: var(--fontsize);
}

.container h2 {
  border-bottom: 2px solid var(--primary-bg-color);
}

@media screen and (min-width: 450px) {
  .container {
    --fontsize: 40px;
  }
}
```

**Example 2 — override multiple variables in the media query** [S1]
A second example modifies multiple variables inside the media query, additionally changing `--primary-bg-color` from the blue hex value to `lightblue` at the larger breakpoint: [S1]
```css
:root {
  --primary-bg-color: #1e90ff;
  --primary-color: #ffffff;
}

body {
  background-color: var(--primary-bg-color);
}

.container {
  --fontsize: 20px;
  color: var(--primary-bg-color);
  background-color: var(--primary-color);
  padding: 15px;
  font-size: var(--fontsize);
}

.container h2 {
  border-bottom: 2px solid var(--primary-bg-color);
}

@media screen and (min-width: 450px) {
  .container {
    --fontsize: 40px;
  }
  :root {
    --primary-bg-color: lightblue;
  }
}
```

**CSS `var()` function reference** [S1]

| Function | Description |
|----------|-------------|
| `var()` | Inserts the value of a CSS variable |

## 🛠️ 적용 사례 (Applied in summary)
The page's applied examples are a responsive card (`.container`): font size scales from 20px to 40px at the 450px breakpoint (Example 1), and in Example 2 the global background color also flips to `lightblue` above that width. No external project/commit applications found in the source.

## 💻 코드 패턴 (Code patterns)
Override a variable at a breakpoint (language: CSS):
```css
.container {
  --fontsize: 20px;
  font-size: var(--fontsize);
}

@media screen and (min-width: 450px) {
  .container {
    --fontsize: 40px;
  }
}
```

## ⚖️ 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:** 0.88
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[CSS Tutorial]]
- **관련 개념:** [[CSS Variables]], [[CSS Variables and JavaScript]], [[CSS Media Queries]], [[CSS @property]]
- **참조 맥락:** Referenced when building responsive designs whose tokens (font sizes, colors) change at viewport breakpoints via custom properties.

## 📚 출처 (Sources)
- [S1] W3Schools — CSS Variables in Media Queries — https://www.w3schools.com/css/css3_variables_mediaqueries.asp

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