---
id: css-rounded-corners
title: "CSS Rounded Corners"
category: "Frontend"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["border-radius", "rounded corners", "CSS3 borders", "border-top-left-radius", "circular shape CSS", "elliptical corners"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.90
created_at: 2026-06-23
updated_at: 2026-06-23
review_reason: ""
merge_history: []
tags: ["css", "web", "frontend", "w3schools", "border-radius", "borders"]
raw_sources: ["https://www.w3schools.com/css/css3_borders.asp"]
applied_in: []
github_commit: ""
---

# [[CSS Rounded Corners]]

## 🎯 한 줄 통찰 (One-line insight)
The `border-radius` property creates rounded corners on elements with a `background-color`, `border`, or `background-image`, and can produce anything from gently rounded boxes to full circles. [S1]

## 🧠 핵심 개념 (Core concepts)
- **`border-radius`** — creates rounded corners on an element. [S1]
- **Where it applies** — it works on elements that have a `background-color`, a `border`, or a `background-image`. [S1]
- **Shorthand** — `border-radius` is shorthand for `border-top-left-radius`, `border-top-right-radius`, `border-bottom-right-radius`, and `border-bottom-left-radius`. [S1]
- **Per-corner control** — 1 to 4 values can be supplied to control corners individually or in groups. [S1]
- **Shapes** — `50%` produces an oval (rectangular elements) or a circle (square elements); a slash separates horizontal and vertical radii for elliptical corners. [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **Value-count pattern** — the number of values supplied (1, 2, 3, or 4) determines which corners they map to, following a top-left → clockwise convention. [S1]
- **Slash pattern** — `horizontal / vertical` defines elliptical corners where the first radius is horizontal and the second is vertical. [S1]
- **Circle/oval pattern** — `border-radius: 50%` turns a square into a circle and a rectangle into an oval. [S1]

## 📖 세부 내용 (Details)
**CSS `border-radius` Property**
The `border-radius` property is used to add rounded corners to an element. It applies to elements that have a `background-color`, a `border`, or a `background-image`. [S1]

The page demonstrates three visual cases: rounded corners with a background color, rounded corners with a border, and rounded corners with a background image. [S1]

```css
#div1 {
  border-radius: 25px;
  background-color: #73AD21;
  padding: 20px;
  width: 200px;
  height: 150px;
}

#div2 {
  border-radius: 25px;
  border: 2px solid #73AD21;
  padding: 20px;
  width: 200px;
  height: 150px;
}

#div3 {
  border-radius: 25px;
  background-image: url(paper.gif);
  background-position: left top;
  background-repeat: repeat;
  padding: 20px;
  width: 200px;
  height: 150px;
}
```

**Tip:** The `border-radius` property is actually a shorthand property for the `border-top-left-radius`, `border-top-right-radius`, `border-bottom-right-radius` and `border-bottom-left-radius` properties. [S1]

**CSS `border-radius` — Specify Each Corner**
The `border-radius` property can have from one to four values, mapping corners as follows: [S1]
- **Four values** — apply to top-left, top-right, bottom-right, bottom-left (in that order). [S1]
- **Three values** — first is top-left, second is top-right and bottom-left, third is bottom-right. [S1]
- **Two values** — first is top-left and bottom-right, second is top-right and bottom-left. [S1]
- **One value** — applies to all four corners equally. [S1]

```css
#div1 {
  border-radius: 15px 50px 30px 5px; /* four values */
 background: #04AA6D;
  width: 200px;
  height: 150px;
}

#div2 {
  border-radius: 15px 50px 30px; /* three values */
  background: #04AA6D;
  width: 200px;
  height: 150px;
}

#div3 {
  border-radius: 15px 50px; /* two values */
  background: #04AA6D;
  width: 200px;
  height: 150px;
}

#div4 {
  border-radius: 15px; /* one value */
  background: #04AA6D;
  width: 200px;
  height: 150px;
}
```

**Elliptical and Circular Shapes**
For elliptical corners, two values are specified, separated by a slash. The first value defines the horizontal radius and the second defines the vertical radius. Setting `border-radius` to `50%` creates an oval shape on rectangular elements or a circular shape on square elements. [S1]

```css
#div1 {
  border-radius: 70px / 30px;
  background: #04AA6D;
  width: 200px;
  height: 150px;
}

#div2 {
  border-radius: 15px / 50px;
  background: #04AA6D;
  width: 200px;
  height: 150px;
}

#div3 {
  border-radius: 50%;
  background: #04AA6D;
  width: 200px;
  height: 150px;
}

#div4 {
border-radius: 50%;
background: #04AA6D;
width: 200px;
height: 200px;
}
```

**CSS Rounded Corners Properties**

| Property | Description |
|----------|-------------|
| `border-radius` | Shorthand for all four border corner radius properties |
| `border-top-left-radius` | Defines the top-left corner border shape |
| `border-top-right-radius` | Defines the top-right corner border shape |
| `border-bottom-right-radius` | Defines the bottom-right corner border shape |
| `border-bottom-left-radius` | Defines the bottom-left corner border shape |

[S1]

## 🛠️ 적용 사례 (Applied in summary)
The page's own examples are the applied cases: rounded boxes using background color/border/image, per-corner radii via 1–4 values, and elliptical/circular shapes via slash syntax and `50%`. No external project/commit applications found in the source.

## 💻 코드 패턴 (Code patterns)
Uniform rounded corners (language: CSS):
```css
selector {
  border-radius: 25px;
}
```
Per-corner radii (top-left, top-right, bottom-right, bottom-left):
```css
selector {
  border-radius: 15px 50px 30px 5px;
}
```
Circle from a square element:
```css
selector {
  border-radius: 50%;
}
```

## ⚖️ 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:** 0.90
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[CSS Tutorial]]
- **관련 개념:** [[CSS Border Images]], [[CSS Multiple Backgrounds]], [[CSS Background Clip]]
- **참조 맥락:** Referenced whenever styling element corners, building rounded cards/buttons, or producing circular avatars.

## 📚 출처 (Sources)
- [S1] W3Schools — CSS Rounded Corners — https://www.w3schools.com/css/css3_borders.asp

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