---
id: css-introduction
title: "CSS Introduction"
category: "Frontend"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["CSS", "Cascading Style Sheets", "stylesheet", "CSS intro", "web styling"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.89
created_at: 2026-06-23
updated_at: 2026-06-23
review_reason: ""
merge_history: []
tags: ["css", "web", "frontend", "styling", "w3schools"]
raw_sources: ["https://www.w3schools.com/css/css_intro.asp"]
applied_in: []
github_commit: ""
---

# [[CSS Introduction]]

## 🎯 한 줄 통찰 (One-line insight)
CSS (Cascading Style Sheets) describes how HTML elements are displayed — controlling the design, layout, and display variations across different devices and screen sizes, ideally from a single external file. [S1]

## 🧠 핵심 개념 (Core concepts)
- **CSS = Cascading Style Sheets** — the language that describes how HTML elements are to be displayed on screen and other media. [S1]
- **Purpose** — CSS defines styles for web pages, including the design, layout, and variations in display for different devices and screen sizes. [S1]
- **Separation of concerns** — HTML holds content/structure; CSS holds presentation. [S1]
- **External stylesheets** — styles can be stored in external `.css` files, so the look of an entire website can be changed by editing just one file. [S1]
- **Efficiency** — CSS can control the layout of multiple web pages all at once. [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **Rule pattern** — a CSS rule targets a selector and sets one or more `property: value;` declarations inside braces: `selector { property: value; }`. [S1]
- **Single source of truth** — one external stylesheet referenced by many pages centralizes styling and avoids per-page duplication. [S1]

## 📖 세부 내용 (Details)
**What is CSS?**
CSS stands for **Cascading Style Sheets**. It describes how HTML elements are to be displayed on various media. [S1]

**Why use CSS?**
CSS is used to define styles for your web pages, including the design, layout, and variations in display for different devices and screen sizes. [S1]

**CSS Saves a Lot of Work**
CSS can control the layout of multiple web pages all at once. With an external stylesheet file, you can change the look of an entire website by changing just one file. [S1]

**Demo example**
The following stylesheet sets the page background color, centers and whitens the heading, and sets the paragraph font: [S1]
```css
body {
  background-color: lightblue;
}

h1 {
  color: white;
  text-align: center;
}

p {
  font-family: verdana;
  font-size: 20px;
}
```

## 🛠️ 적용 사례 (Applied in summary)
The demo stylesheet above is the page's own applied example: a complete set of rules styling `body`, `h1`, and `p`. No external project/commit applications found in the source.

## 💻 코드 패턴 (Code patterns)
Basic CSS rule (language: CSS):
```css
selector {
  property: value;
  property: value;
}
```
Concrete example:
```css
h1 {
  color: white;
  text-align: center;
}
```

## ⚖️ 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:** 0.89
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[CSS Tutorial]]
- **관련 개념:** [[CSS Syntax]], [[CSS Selectors]], [[CSS Add External]], [[HTML CSS]]
- **참조 맥락:** The entry point referenced whenever styling the presentation of any HTML page.

## 📚 출처 (Sources)
- [S1] W3Schools — CSS Introduction — https://www.w3schools.com/css/css_intro.asp

## 📝 변경 이력 (Change history)
- 2026-06-23: Initial draft synthesized from the W3Schools "CSS Introduction" page (Astra wiki-curation, P-Reinforce v3.1 format).