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-horizontal-align
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title: "CSS Horizontal Align"
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category: "Frontend"
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status: "draft"
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verification_status: "conceptual"
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canonical_id: ""
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aliases: ["horizontal align", "margin auto", "center block element", "center image", "left right align"]
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duplicate_of: ""
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source_trust_level: "B"
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confidence_score: 0.89
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created_at: 2026-06-23
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updated_at: 2026-06-23
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review_reason: ""
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merge_history: []
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tags: ["css", "web", "frontend", "w3schools", "alignment", "layout"]
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raw_sources: ["https://www.w3schools.com/css/css_align_horizontal.asp"]
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applied_in: []
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github_commit: ""
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---
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# [[CSS Horizontal Align]]
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## 🎯 한 줄 통찰 (One-line insight)
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Horizontal alignment in CSS depends on the element: `margin: auto` (with a width) centers block elements, `text-align: center` centers text, `auto` left/right margins center images, and `position: absolute` or `float` push elements to the left or right. [S1]
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## 🧠 핵심 개념 (Core concepts)
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- **Center block elements with `margin: auto`** — used to horizontally center a block-level element like `<div>`. [S1]
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- **Width is required for margin auto** — the example sets `width: 50%`; centering with `margin: auto` needs a defined width to take effect. [S1]
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- **Center text with `text-align: center`** — used to center text inside a block-level element. [S1]
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- **Center an image** — set `margin-left` and `margin-right` to `auto` and turn the image into a `block` element. [S1]
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- **Directional alignment** — `position: absolute` (with `right`/`left`) or `float` push an element to one side. [S1]
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- **Absolute positioning caveat** — absolute positioned elements are removed from the normal flow, and can overlap other elements. [S1]
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## 🧩 추출된 패턴 (Extracted patterns)
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- **Block centering pattern** — `margin: auto` + an explicit `width`. [S1]
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- **Image centering pattern** — `display: block` + `margin-left: auto` + `margin-right: auto`. [S1]
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- **Right-align patterns** — `position: absolute; right: 0px;` (removed from flow) or `float: right;` (stays in flow). [S1]
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## 📖 세부 내용 (Details)
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**Center Align Block Elements**
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Use `margin: auto;`, to horizontally center a block-level element (like `<div>`). [S1]
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```css
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.center {
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margin: auto;
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width: 50%;
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border: 3px solid green;
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padding: 10px;
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}
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```
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**Center Align Text**
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To center the text inside a block-level element, use `text-align: center;`. [S1]
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```css
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p {
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text-align: center;
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}
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```
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**Center Align an Image**
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To center an image, set `margin-left` and `margin-right` to `auto`, and also turn the image into a `block` element. [S1]
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```css
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img {
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display: block;
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margin-left: auto;
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margin-right: auto;
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width: 40%;
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}
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```
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**Left and Right Align — Using `position`**
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Another method for aligning elements is to use `position: absolute;`. Note: absolute positioned elements are removed from the normal flow, and can overlap other elements. [S1]
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```css
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.right {
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position: absolute;
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right: 0px;
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width: 300px;
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border: 3px solid green;
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padding: 10px;
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}
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```
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**Left and Right Align — Using `float`**
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Another method for aligning an element to the left or right is to use the `float` property. [S1]
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```css
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.right {
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float: right;
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width: 300px;
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border: 3px solid green;
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padding: 10px;
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}
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```
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## 🛠️ 적용 사례 (Applied in summary)
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The page's own applied examples are: centering a block `div` with `margin: auto`, centering paragraph text, centering an image, right-aligning with `position: absolute`, and right-aligning with `float`. No external project/commit applications found in the source.
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## 💻 코드 패턴 (Code patterns)
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Center a block element (language: CSS):
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```css
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.center {
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margin: auto;
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width: 50%;
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}
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```
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Center an image:
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```css
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img {
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display: block;
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margin-left: auto;
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margin-right: auto;
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width: 40%;
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}
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```
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## ⚖️ 비교 및 선택 기준 (Comparison & decision criteria)
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- **`position: absolute` vs `float` for right alignment** — both push an element to the right, but `position: absolute` removes the element from the normal flow (it can overlap other elements), whereas `float: right` keeps it in the flow. [S1]
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- **By content type** — block elements → `margin: auto`; text → `text-align: center`; images → block + auto side margins. [S1]
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## ⚖️ 모순 및 업데이트 (Contradictions & updates)
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No contradictions found in the source.
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## ✅ 검증 상태 및 신뢰도
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- **상태:** draft
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- **검증 단계:** conceptual (실제 적용 사례 발견 시 applied/validated로 승격 가능)
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- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
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- **신뢰 점수:** 0.89
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- **중복 검사 결과:** 신규 생성 (New discovery)
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## 🔗 지식 그래프 (Knowledge Graph)
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- **상위/루트:** [[CSS Tutorial]]
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- **관련 개념:** [[CSS Center Align]], [[CSS Vertical Align]], [[CSS Float Examples]], [[CSS Position]]
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- **참조 맥락:** Referenced when horizontally centering or side-aligning blocks, text, and images.
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## 📚 출처 (Sources)
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- [S1] W3Schools — CSS Horizontal Align — https://www.w3schools.com/css/css_align_horizontal.asp
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## 📝 변경 이력 (Change history)
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- 2026-06-23: Initial draft synthesized from the W3Schools "CSS Horizontal Align" page (Astra wiki-curation, P-Reinforce v3.1 format).
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