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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>
112 lines
5.2 KiB
Markdown
112 lines
5.2 KiB
Markdown
---
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id: css-units
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title: "CSS Units"
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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: ["CSS units", "CSS length", "length values", "absolute units", "relative units"]
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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", "units", "length", "measurement"]
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raw_sources: ["https://www.w3schools.com/css/css_units.asp"]
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applied_in: []
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github_commit: ""
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---
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# [[CSS Units]]
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## 🎯 한 줄 통찰 (One-line insight)
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CSS units express the length of properties such as `font-size`, `width`, `margin`, `padding`, and `border`, and they split into two families: absolute units (fixed) and relative units (scale with parent, root, or viewport). [S1]
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## 🧠 핵심 개념 (Core concepts)
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- **Length values** — several CSS properties take "length" values, such as `font-size`, `width`, `margin`, `padding`, and `border`. [S1]
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- **No whitespace rule** — there must be no space between the number and the unit (e.g., `10px`, not `10 px`); however, if the value is `0`, the unit can be omitted. [S1]
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- **Two categories** — Absolute units are fixed lengths; Relative units scale based on a parent element, the root element, or the viewport. [S1]
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## 🧩 추출된 패턴 (Extracted patterns)
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- **Absolute for print, relative for screen** — absolute units suit fixed/print contexts; relative units (`em`, `rem`) scale better across screen sizes. [S1]
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- **Omit unit only for zero** — `0` is the single value where the unit may be dropped. [S1]
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## 📖 세부 내용 (Details)
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**Introduction**
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Several CSS properties take "length" values, such as `font-size`, `width`, `margin`, `padding`, and `border`. There must be no whitespace between the number and the unit; however, if the value is `0`, the unit can be omitted. [S1]
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CSS has two types of length units: **Absolute** and **Relative**. [S1]
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**Absolute Lengths**
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Absolute length units are fixed lengths. [S1]
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| Unit | Description |
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| --- | --- |
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| `cm` | centimeters [S1] |
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| `mm` | millimeters [S1] |
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| `in` | inches (1in = 96px = 2.54cm) [S1] |
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| `px` | pixels (1px = 1/96th of 1in) — the most-used absolute unit for screens [S1] |
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| `pt` | points (1pt = 1/72 of 1in) — a typographical unit [S1] |
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| `pc` | picas (1pc = 12 pt) — a print unit [S1] |
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A typical absolute-unit usage sets font sizes in pixels: [S1]
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```css
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h1 { font-size: 40px; }
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h2 { font-size: 30px; }
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p { font-size: 17px; }
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```
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**Relative Lengths**
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Relative length units specify a length relative to another length property, and scale better between different screen sizes. [S1]
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| Unit | Description |
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| --- | --- |
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| `em` | Relative to the font-size of the element [S1] |
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| `ex` | Relative to the x-height of the current font (height of lowercase "x") [S1] |
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| `ch` | Relative to the width of the "0" (zero) character [S1] |
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| `rem` | Relative to the font-size of the root element [S1] |
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| `vw` | Relative to 1% of the width of the viewport [S1] |
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| `vh` | Relative to 1% of the height of the viewport [S1] |
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| `vmin` | Relative to 1% of the viewport's smaller dimension [S1] |
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| `vmax` | Relative to 1% of the viewport's larger dimension [S1] |
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| `%` | Relative to the size of the parent element [S1] |
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**Tip:** The `em` and `rem` units are perfect for creating scalable and responsive websites. [S1]
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## 🛠️ 적용 사례 (Applied in summary)
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The page's applied case is the pixel font-size example styling `h1`, `h2`, and `p`. Detailed per-family examples live on the dedicated [[CSS Absolute Units]] and [[CSS Relative Units]] pages. No external project/commit applications found in the source.
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## 💻 코드 패턴 (Code patterns)
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Pixel (absolute) font sizing (language: CSS):
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```css
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h1 { font-size: 40px; }
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p { font-size: 17px; }
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```
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## ⚖️ 비교 및 선택 기준 (Comparison & decision criteria)
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- **Absolute units** (`cm`, `mm`, `in`, `px`, `pt`, `pc`) — fixed lengths; pixels are the most-used for screens, the rest are mainly for print. [S1]
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- **Relative units** (`em`, `ex`, `ch`, `rem`, `vw`, `vh`, `vmin`, `vmax`, `%`) — scale relative to another length, so they adapt across screen sizes; `em` and `rem` are recommended for scalable, responsive sites. [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 Absolute Units]], [[CSS Relative Units]], [[CSS Font Size]]
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- **참조 맥락:** Referenced whenever specifying any length value (size, spacing, borders) in CSS.
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## 📚 출처 (Sources)
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- [S1] W3Schools — CSS Units — https://www.w3schools.com/css/css_units.asp
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## 📝 변경 이력 (Change history)
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- 2026-06-23: Initial draft synthesized from the W3Schools "CSS Units" page (Astra wiki-curation, P-Reinforce v3.1 format).
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