---
id: w3css-flexbox
title: "W3CSS Flexbox"
category: "Programming_Language"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["w3-flex", "CSS Flexbox", "perfect centering", "W3.CSS 플렉스박스"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.88
created_at: 2026-07-04
updated_at: 2026-07-04
review_reason: ""
merge_history: []
tags: ["w3css", "css-framework", "w3schools", "flexbox"]
raw_sources: ["https://www.w3schools.com/w3css/w3css_flexbox.asp"]
applied_in: []
github_commit: ""
---

# [[W3CSS Flexbox]]

## 🎯 한 줄 통찰 (One-line insight)
"Perfect centering" — a notoriously fiddly CSS problem historically — collapses to exactly TWO properties in flexbox: `justify-content:center` (horizontal) plus `align-items:center` (vertical) on the SAME container, which the source explicitly calls out as "the solution" to a common style problem, contrasting flexbox's simplicity against older centering hacks. [S1]

## 🧠 핵심 개념 (Core concepts)
- **`w3-flex`** (W3.CSS 5.0+) — one-dimensional flex container (row OR column, unlike grid's row AND column). [S1]
- **`flex-direction`** — `row` (default, left-to-right), `column`, `row-reverse`, `column-reverse`. [S1]
- **`flex-wrap`** — `nowrap` (default), `wrap`, `wrap-reverse`. [S1]
- **`justify-content`** — aligns items along the main axis: `center`, `flex-start`, `flex-end`, `space-around`, `space-between`, `space-evenly`. [S1]
- **`align-items`** — aligns items along the cross axis: `center`, `flex-start`, `flex-end`, `stretch` (default), `baseline`. [S1]
- **`align-content`** — aligns entire WRAPPED LINES (not individual items) when `flex-wrap:wrap` is active; distinct from `align-items`. [S1]
- **Perfect centering recipe** — `justify-content:center` + `align-items:center` together on one flex container. [S1]

## 📖 세부 내용 (Details)
- Basic flex container: `<div class="w3-flex" style="gap:8px"><div>1</div><div>2</div><div>3</div></div>`. [S1]
- Reversed direction: `<div class="w3-flex" style="flex-direction:row-reverse">`. [S1]
- Baseline alignment (items with different font sizes align by text baseline, not box edge): `<div class="w3-flex" style="align-items:baseline">`. [S1]
- Perfect centering: `<div class="w3-flex" style="height:300px;justify-content:center;align-items:center">`. [S1]

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
- **align-content와 align-items의 차이**: align-items는 개별 아이템을, align-content는 줄바꿈된 전체 라인을 정렬한다는 점이 구분됨(flex-wrap:wrap 상태에서만 의미가 있음). [S1]

## 🛠️ 적용 사례 (Applied in summary)
현재 발견된 실제 적용 사례가 없습니다 — justify-content+align-items를 함께 center로 설정하는 "완벽한 중앙 정렬" 레시피가 실전에서 가장 자주 쓰이는 플렉스박스 패턴이다. [S1]

## 💻 코드 패턴 (Code patterns)
Perfect centering with two flexbox properties (HTML/CSS):
```html
<div class="w3-flex" style="height:300px;justify-content:center;align-items:center">
  <div>1</div><div>2</div><div>3</div>
</div>
```

## ✅ 검증 상태 및 신뢰도
- **상태:** draft
- **검증 단계:** conceptual
- **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:** [[W3.CSS Tutorial]]
- **관련 개념:** [[W3CSS Grid]], [[W3CSS Flex Items]]
- **참조 맥락:** 1차원 레이아웃 컨테이너 — 개별 플렉스 아이템 속성(Flex Items) 챕터로 이어짐.

## 📚 출처 (Sources)
- [S1] W3Schools — W3.CSS Flexbox — https://www.w3schools.com/w3css/w3css_flexbox.asp

## 📝 변경 이력 (Change history)
- 2026-07-04: Initial draft synthesized from the W3Schools "W3.CSS Flexbox" page (Astra wiki-curation, P-Reinforce v3.1 format).