---
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).