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-content-pseudo-elements
+title: "CSS Content Pseudo-elements"
+category: "Frontend"
+status: "draft"
+verification_status: "conceptual"
+canonical_id: ""
+aliases: ["::before", "::after", "::marker", "::selection", "::backdrop", "content pseudo-elements", "generated content"]
+duplicate_of: ""
+source_trust_level: "B"
+confidence_score: 0.87
+created_at: 2026-06-23
+updated_at: 2026-06-23
+review_reason: ""
+merge_history: []
+tags: ["css", "web", "frontend", "w3schools", "pseudo-elements", "content"]
+raw_sources: ["https://www.w3schools.com/css/css_pseudo_elements_content.asp"]
+applied_in: []
+github_commit: ""
+---
+
+# [[CSS Content Pseudo-elements]]
+
+## 🎯 한 줄 통찰 (One-line insight)
+Content pseudo-elements insert or style generated parts of an element — `::before`/`::after` add content, while `::marker`, `::selection`, and `::backdrop` style list markers, selected text, and dialog backdrops. [S1]
+
+## 🧠 핵심 개념 (Core concepts)
+- **`::before`** — inserts some content before the content of a specified element, via the `content` property. [S1]
+- **`::after`** — inserts some content after the content of a specified element, via the `content` property. [S1]
+- **`::marker`** — styles the list item markers. [S1]
+- **`::selection`** — styles the part of a text that is selected by a user. [S1]
+- **`::backdrop`** — styles the viewbox behind a dialog box or popover element. [S1]
+
+## 🧩 추출된 패턴 (Extracted patterns)
+- **Generated content** — `::before`/`::after` paired with the `content` property inject images or text that are not in the HTML. [S1]
+- **Marker styling** — `::marker` recolors and resizes list bullets/numbers without changing list structure. [S1]
+- **User-state styling** — `::selection` reacts to the user's text selection. [S1]
+
+## 📖 세부 내용 (Details)
+**The `::before` pseudo-element** [S1]
+The `::before` pseudo-element is used to insert some content before the content of a specified element. Here it inserts an image before each `<h3>`:
+```css
+h3::before {
+  content: url(smiley.gif);
+}
+```
+
+**The `::after` pseudo-element** [S1]
+The `::after` pseudo-element is used to insert some content after the content of a specified element:
+```css
+h3::after {
+  content: url(smiley.gif);
+}
+```
+
+**The `::marker` pseudo-element** [S1]
+The `::marker` pseudo-element is used to style the list item markers:
+```css
+::marker {
+  color: red;
+  font-size: 23px;
+}
+```
+
+**The `::selection` pseudo-element** [S1]
+The `::selection` pseudo-element is used to style the part of a text that is selected by a user:
+```css
+::selection {
+  color: red;
+  background: yellow;
+}
+```
+
+**The `::backdrop` pseudo-element** [S1]
+The `::backdrop` pseudo-element is used to style the viewbox behind a dialog box or popover element:
+```css
+dialog::backdrop {
+  background-color: lightgreen;
+}
+```
+
+## 🛠️ 적용 사례 (Applied in summary)
+The page's applied examples are the smiley image inserted before/after `<h3>`, recolored/enlarged list markers, red-on-yellow text selection, and a light-green dialog backdrop. No external project/commit applications found in the source.
+
+## 💻 코드 패턴 (Code patterns)
+Insert content before an element (language: CSS):
+```css
+h3::before {
+  content: url(smiley.gif);
+}
+```
+Style user-selected text (language: CSS):
+```css
+::selection {
+  color: red;
+  background: yellow;
+}
+```
+
+## ⚖️ 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:** 0.87
+- **중복 검사 결과:** 신규 생성 (New discovery)
+
+## 🔗 지식 그래프 (Knowledge Graph)
+- **상위/루트:** [[CSS Tutorial]]
+- **관련 개념:** [[CSS Pseudo-elements]], [[CSS Text Pseudo-elements]], [[CSS Lists]]
+- **참조 맥락:** Referenced when inserting generated content or styling markers, selections, and dialog backdrops.
+
+## 📚 출처 (Sources)
+- [S1] W3Schools — CSS Content Pseudo-elements — https://www.w3schools.com/css/css_pseudo_elements_content.asp
+
+## 📝 변경 이력 (Change history)
+- 2026-06-23: Initial draft synthesized from the W3Schools "CSS Content Pseudo-elements" page (Astra wiki-curation, P-Reinforce v3.1 format).