2nd/10_Wiki/Topic_CSS/CSS_Property_Rule.md

---
id: css-property
title: "CSS @property"
category: "Frontend"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["@property rule", "CSS at-property", "typed custom properties", "registered custom properties", "CSS property syntax inherits initial-value"]
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", "css-variables", "at-rules", "animation"]
raw_sources: ["https://www.w3schools.com/css/css3_property.asp"]
applied_in: []
github_commit: ""
---

# [[CSS @property]]

## 🎯 한 줄 통찰 (One-line insight)
`@property` defines custom CSS properties (CSS variables) directly in the stylesheet — without JavaScript — adding data-type checking, a required default value, and explicit control over inheritance. [S1]

## 🧠 핵심 개념 (Core concepts)
- **What it is** — `@property` is used to define custom CSS properties (CSS variables) directly in the stylesheet without having to run any JavaScript. [S1]
- **Data type checking** — ensures custom properties are used correctly via a declared `syntax` (e.g. `"<color>"`). [S1]
- **Default value requirement** — `initial-value` provides a fallback if an invalid value is assigned. [S1]
- **Inheritance control** — `inherits: true | false` gives full control over whether the value inherits. [S1]
- **Consumed with `var()`** — once defined, the property is used like any custom property, e.g. `background-color: var(--myColor);`. [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **Typed declaration pattern** — `@property --name { syntax: "<type>"; inherits: <bool>; initial-value: <value>; }`. [S1]
- **Invalid-value fallback** — when a value violates the declared `syntax` (e.g. assigning `2` where a `<color>` is expected), the property falls back to its `initial-value` instead of breaking. [S1]
- **Animatable custom colors** — declaring color custom properties with `@property` enables them to participate in transitions/animations (e.g. a gradient that animates between `--startColor` and `--endColor`). [S1]

## 📖 세부 내용 (Details)
`@property` is used to define custom CSS properties (CSS variables) directly in the stylesheet without having to run any JavaScript, with data type checking, default values, and inheritance control. [S1]

**Basic syntax** [S1]
```css
@property --myColor {
  syntax: "<color>";
  inherits: true;
  initial-value: lightgray;
}
```
Usage with the `var()` function: [S1]
```css
body {
  background-color: var(--myColor);
}
```

**Example 1 — two custom properties** [S1]
```css
@property --my-bg-color {
  syntax: "<color>";
  inherits: true;
  initial-value: lightgray;
}

@property --my-txt-color {
  syntax: "<color>";
  inherits: true;
  initial-value: darkblue;
}

div {
  width: 300px;
  height: 150px;
  padding: 15px;
  background-color: var(--my-bg-color);
  color: var(--my-txt-color);
}
```

**Example 2 — overriding custom properties per class** [S1]
```css
@property --my-bg-color {
  syntax: "<color>";
  inherits: true;
  initial-value: lightgray;
}

div {
  width: 300px;
  height: 150px;
  padding: 15px;
  background-color: var(--my-bg-color);
}

.fresh {
  --my-bg-color: #ff6347;
}

.nature {
  --my-bg-color: rgb(120, 180, 30);
}
```

**Example 3 — type checking with an invalid value** [S1]
Here `.nature` assigns `2`, which is not a valid `<color>`, so the property falls back to its `initial-value`: [S1]
```css
@property --my-bg-color {
  syntax: "<color>";
  inherits: true;
  initial-value: lightgray;
}

div {
  width: 300px;
  height: 150px;
  padding: 15px;
  background-color: var(--my-bg-color);
}

.fresh {
  --my-bg-color: #ff6347;
}

.nature {
  --my-bg-color: 2;
}
```

**Example 4 — `inherits: false`** [S1]
```css
@property --my-bg-color {
  syntax: "<color>";
  inherits: false;
  initial-value: lightgray;
}
```

**Example 5 — `inherits: true`** [S1]
```css
@property --my-bg-color {
  syntax: "<color>";
  inherits: true;
  initial-value: lightgray;
}
```

**Example 6 — animated gradient colors** [S1]
```css
@property --startColor {
  syntax: "<color>";
  initial-value: #EADEDB;
  inherits: false;
}

@property --endColor {
  syntax: "<color>";
  initial-value: #BC70A4;
  inherits: false;
}
```

**Key benefits listed by the source** [S1]
- **Data type checking** ensures custom properties are used correctly.
- **Default value requirement** provides a fallback if invalid values are assigned.
- **Inheritance control** gives full control over value inheritance behavior.

## 🛠️ 적용 사례 (Applied in summary)
The page's applied examples progress from declaring typed color properties (Example 1), overriding them per class `.fresh` / `.nature` (Example 2), demonstrating fallback to `initial-value` on an invalid `2` (Example 3), contrasting `inherits: false` vs `inherits: true` (Examples 4–5), and finally declaring `--startColor`/`--endColor` for an animated gradient (Example 6). No external project/commit applications found in the source.

## 💻 코드 패턴 (Code patterns)
Define a typed custom property (language: CSS):
```css
@property --my-bg-color {
  syntax: "<color>";
  inherits: true;
  initial-value: lightgray;
}
```
Consume it (language: CSS):
```css
div {
  background-color: var(--my-bg-color);
}
```

## ⚖️ 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 Variables]], [[CSS Variables and JavaScript]], [[CSS Variables in Media Queries]], [[CSS var Function]]
- **참조 맥락:** Referenced when custom properties need type safety, guaranteed fallbacks, or animation support without JavaScript.

## 📚 출처 (Sources)
- [S1] W3Schools — CSS @property — https://www.w3schools.com/css/css3_property.asp

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