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>
2026-06-23 19:21:18 +09:00
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+---
+id: css-pseudo-elements
+title: "CSS Pseudo-elements"
+category: "Frontend"
+status: "draft"
+verification_status: "conceptual"
+canonical_id: ""
+aliases: ["pseudo-elements", "::before", "::after", "::first-line", "::marker", "double-colon selectors"]
+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", "pseudo-elements", "selectors"]
+raw_sources: ["https://www.w3schools.com/css/css_pseudo_elements.asp"]
+applied_in: []
+github_commit: ""
+---
+
+# [[CSS Pseudo-elements]]
+
+## 🎯 한 줄 통찰 (One-line insight)
+A CSS pseudo-element is a keyword added to a selector that lets you style a specific part of an element — the first line, the first letter, inserted content, list markers, selected text, or a dialog backdrop. [S1]
+
+## 🧠 핵심 개념 (Core concepts)
+- **Definition** — A CSS pseudo-element is a keyword that can be added to a selector, to style a specific part of an element. [S1]
+- **Double-colon syntax** — pseudo-elements are written with `::` after the selector. [S1]
+- **Two families** — text pseudo-elements (`::first-line`, `::first-letter`) and content pseudo-elements (`::before`, `::after`, `::marker`, `::selection`, `::backdrop`). [S1]
+
+## 🧩 추출된 패턴 (Extracted patterns)
+- **Style a part, not the whole** — pseudo-elements address sub-parts of an element (a line, a letter, generated content) rather than the element as a whole. [S1]
+- **Syntax pattern** — `selector::pseudo-element-name { CSS properties }`. [S1]
+
+## 📖 세부 내용 (Details)
+**Definition** [S1]
+A CSS pseudo-element is a keyword that can be added to a selector, to style a specific part of an element. Common uses include:
+- Styling the first letter or first line of an element
+- Inserting content before or after an element
+- Styling list item markers
+- Styling user-selected portions of an element
+- Styling the viewbox behind a dialog box
+
+**Syntax** [S1]
+```css
+selector::pseudo-element-name {
+  CSS properties
+}
+```
+
+**Text pseudo-elements** [S1]
+
+| Pseudo-element | Description |
+| --- | --- |
+| `::first-line` | Style the first line of text |
+| `::first-letter` | Style the first letter of text |
+
+**Content pseudo-elements** [S1]
+
+| Pseudo-element | Description |
+| --- | --- |
+| `::before` | Insert content before an element |
+| `::after` | Insert content after an element |
+| `::marker` | Style list item markers |
+| `::selection` | Style user-selected text |
+| `::backdrop` | Style dialog backdrop |
+
+The source references a complete CSS Pseudo-elements Reference for the full list. [S1]
+
+## 🛠️ 적용 사례 (Applied in summary)
+This page is an overview/index; the detailed applied examples live on the dedicated text and content pseudo-element pages. No external project/commit applications found in the source.
+
+## 💻 코드 패턴 (Code patterns)
+Pseudo-element syntax (language: CSS):
+```css
+selector::pseudo-element-name {
+  CSS properties
+}
+```
+
+## ⚖️ 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 Text Pseudo-elements]], [[CSS Content Pseudo-elements]], [[CSS Structural Pseudo-classes]]
+- **참조 맥락:** The entry point whenever styling a specific part of an element rather than the whole.
+
+## 📚 출처 (Sources)
+- [S1] W3Schools — CSS Pseudo-elements — https://www.w3schools.com/css/css_pseudo_elements.asp
+
+## 📝 변경 이력 (Change history)
+- 2026-06-23: Initial draft synthesized from the W3Schools "CSS Pseudo-elements" page (Astra wiki-curation, P-Reinforce v3.1 format).