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• 句法
• 范例
• 规范
• 浏览器兼容性
• 另请参阅
• 相关话题

var() CSS function can be used to insert the value of a custom property (sometimes called a "CSS variable") instead of any part of a value of another property.

The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.

var() function cannot be used in property names, selectors or anything else besides property values. (Doing so usually produces invalid syntax, or else a value whose meaning has no connection to the variable.)

句法

The first argument to the function is the name of the custom property to be substituted. An optional second argument to the function serves as a fallback value. If the custom property referenced by the first argument is invalid, the function uses the second value.

var( <custom-property-name> , <declaration-value>? )
				

注意： The syntax of the fallback, like that of custom properties, allows commas. For example, var(--foo, red, blue) defines a fallback of red, blue ; that is, anything between the first comma and the end of the function is considered a fallback value.

值

<custom-property-name>

A custom property’s name represented by an identifier that starts with two dashes. Custom properties are solely for use by authors and users; CSS will never give them a meaning beyond what is presented here.

<declaration-value>

The custom property's fallback value, which is used in case the custom property is invalid in the used context. This value may contain any character except some characters with special meaning like newlines, unmatched closing brackets, i.e. ) , ] ，或 } , top-level semicolons, or exclamation marks.

范例

Using a custom property set on :root

:root {
  --main-bg-color: pink;
}
body {
  background-color: var(--main-bg-color);
}
					

Custom properties with fallbacks for use when the property has not been set

/* Fallback */
/* In the component’s style: */
.component .header {
  color: var(--header-color, blue); /* header-color isn’t set, and so remains blue, the fallback value */
}
.component .text {
  color: var(--text-color, black);
}
/* In the larger application’s style: */
.component {
  --text-color: #080;
}
					

规范

规范	状态	注释
CSS Custom Properties for Cascading Variables Module Level 1 The definition of 'var()' in that specification.	候选推荐	初始定义

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 更新 GitHub 上的兼容性数据

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
var()	Chrome 完整支持 49	Edge 完整支持 15	Firefox 完整支持 31	IE 不支持 No	Opera 完整支持 36	Safari 完整支持 9.1	WebView Android 完整支持 50	Chrome Android 完整支持 49	Firefox Android 完整支持 31	Opera Android 完整支持 36	Safari iOS 完整支持 9.3	Samsung Internet Android 完整支持 5.0

图例

完整支持

完整支持

不支持

不支持

用户必须明确启用此特征。

用户必须明确启用此特征。

另请参阅

• env(…) – read‑only environment variables controlled by the user‑agent.
• Using CSS variables

元数据

• 最后修改： Nov 4, 2020

相关话题

1. CSS
2. CSS 参考