docs(10_Wiki): W3Schools 위키화 — HTML/CSS/JavaScript(core)

W3Schools 튜토리얼을 P-Reinforce v3.1 포맷으로 위키화(영어 본문, 한/영 섹션 헤더).
- Topic_HTML: 59문서 (튜토리얼+예제, 레퍼런스/메타 제외)
- Topic_CSS: 190문서 (메인 + Advanced/Flexbox/Grid/RWD 전체)
- Topic_JavaScript: 120문서 (코어 언어; Temporal/DOM상세/BOM/WebAPI/AJAX/jQuery/Graphics 등은 후속)
각 폴더 00_INDEX.md(MOC) 포함. 코드 verbatim, 미확인분은 "Not found in source" 표기.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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---
id: css-flexbox-responsive
title: "CSS Flexbox Responsive"
category: "Frontend"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["responsive flexbox", "flexbox media queries", "flex-direction breakpoint", "responsive flex layout", "flex responsive columns"]
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", "flexbox", "responsive"]
raw_sources: ["https://www.w3schools.com/css/css3_flexbox_responsive.asp"]
applied_in: []
github_commit: ""
---
# [[CSS Flexbox Responsive]]
## 🎯 한 줄 통찰 (One-line insight)
Responsive Flexbox layouts adapt across screen sizes by using media queries to either change `flex-direction` from `row` to `column`, or adjust the percentage of the `flex` property on wrapping items. [S1]
## 🧠 핵심 개념 (Core concepts)
- **Two responsive techniques** — change `flex-direction`, or change the `flex` percentage at a breakpoint. [S1]
- **Direction switch** — switch `flex-direction` from `row` to `column` at a breakpoint to convert a multi-column layout into a one-column layout on small screens. [S1]
- **Flex percentage switch** — change the `flex` percentage of items (requires `flex-wrap: wrap`) to reflow columns at a breakpoint. [S1]
## 🧩 추출된 패턴 (Extracted patterns)
- **Breakpoint via `@media`** — both techniques wrap the layout change in a `@media (max-width: 600px)` query. [S1]
- **`flex-wrap: wrap` enables percentage reflow** — required on the container when using the `flex` percentage method. [S1]
## 📖 세부 내용 (Details)
**Method 1: Changing Flex Direction**
If you want to create a three-column layout for large screen sizes, and a one-column layout for small screen sizes (such as phones), you can change the `flex-direction` from `row` to `column` at a specific breakpoint. [S1]
```css
.flex-container {
display: flex;
flex-direction: row;
}
.flex-item {
background-color: #f1f1f1;
padding: 10px;
font-size: 30px;
text-align: center;
width: 100%;
}
/* Make a one column-layout instead of three-column layout */
@media (max-width: 600px) {
.flex-container {
flex-direction: column;
}
}
```
**Method 2: Modifying the Flex Property**
An alternative technique involves changing the percentage of the `flex` property of the flex items to create different layouts for different screen sizes, requiring `flex-wrap: wrap;` on the container. [S1]
```css
.flex-container {
display: flex;
flex-wrap: wrap;
}
.flex-item {
background-color: #f1f1f1;
padding: 10px;
text-align: center;
font-size: 30px;
flex: 33.3%;
}
/* Make a one column-layout instead of a three-column layout */
@media (max-width: 600px) {
.flex-item {
flex: 100%;
}
}
```
The page also references two additional examples — a responsive image gallery and a responsive website — both implementing flexbox with media queries for layout adaptation. The full source code of those two examples was not found inline on the page (presented behind "Try it Yourself" links).
## 🛠️ 적용 사례 (Applied in summary)
The page applies both techniques to a `.flex-container`/`.flex-item` pair, reflowing a three-column layout into one column below a 600px breakpoint. No external project/commit applications found in the source.
## 💻 코드 패턴 (Code patterns)
Responsive reflow via flex-direction (language: CSS):
```css
.flex-container {
display: flex;
flex-direction: row;
}
@media (max-width: 600px) {
.flex-container {
flex-direction: column;
}
}
```
## ⚖️ 비교 및 선택 기준 (Comparison & decision criteria)
- **Change `flex-direction`** — simplest when each item is full-width (`width: 100%`) and you just need to stack them vertically on small screens. [S1]
- **Change `flex` percentage** — use when items wrap (`flex-wrap: wrap`) and you want to control how many columns appear at each breakpoint (e.g., `flex: 33.3%` to `flex: 100%`). [S1]
## ⚖️ 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 Flexbox Justify Content]], [[CSS Flexbox Align Items]], [[CSS Flex Items]]
- **참조 맥락:** Referenced whenever building flexbox layouts that must adapt across desktop and mobile screen sizes.
## 📚 출처 (Sources)
- [S1] W3Schools — CSS Flexbox Responsive — https://www.w3schools.com/css/css3_flexbox_responsive.asp
## 📝 변경 이력 (Change history)
- 2026-06-23: Initial draft synthesized from the W3Schools "CSS Flexbox Responsive" page (Astra wiki-curation, P-Reinforce v3.1 format).