The 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.

var(--header-color, blue);

The 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.)

Syntax

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> ]? )

Note: 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.

Values

<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. ), ], or }, top-level semicolons, or exclamation marks.

Examples

:root {
  --main-bg-color: pink;
}

body {
  background-color: var(--main-bg-color);
}
/* 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;
}

Specifications

Specification Status Comment
CSS Custom Properties for Cascading Variables Module Level 1
The definition of 'var()' in that specification.
Candidate Recommendation Initial definition

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidiOS SafariSamsung Internet
Basic support
Experimental
Chrome Full support 49
Full support 49
Full support 48
Disabled
Disabled From version 48: this feature is behind the Enable experimental Web Platform features preference. To change preferences in Chrome, visit chrome://flags.
Edge Full support 15Firefox Full support 31
Full support 31
No support 29 — 55
Notes Disabled
Notes From Firefox 29 until Firefox 31, this feature was implemented by the var-variablename syntax.
Disabled From version 29 until version 55 (exclusive): this feature is behind the layout.css.variables.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
IE No support NoOpera Full support 36Safari Full support YesWebView Android Full support 50Chrome Android ? Edge Mobile Full support 15Firefox Android Full support 31
Full support 31
No support 29 — 55
Notes Disabled
Notes From Firefox 29 until Firefox 31, this feature was implemented by the var-variablename syntax.
Disabled From version 29 until version 55 (exclusive): this feature is behind the layout.css.variables.enabled preference (needs to be set to true). To change preferences in Firefox, visit about:config.
Opera Android Full support 37Safari iOS Full support YesSamsung Internet Android ?

Legend

Full support  
Full support
No support  
No support
Compatibility unknown  
Compatibility unknown
Experimental. Expect behavior to change in the future.
Experimental. Expect behavior to change in the future.
See implementation notes.
See implementation notes.
User must explicitly enable this feature.
User must explicitly enable this feature.

See also