Custom properties (--*): CSS variables
Baseline
Widely available
This feature is well established and works across many devices and browser versions. Itās been available across browsers since āØApril 2017ā©.
Property names that are prefixed with --, like --example-name, represent custom properties that contain a value that can be used in other declarations using the var() function.
Custom properties are scoped to the element(s) they are declared on, and participate in the cascade: the value of such a custom property is that from the declaration decided by the cascading algorithm.
| Initial value | see prose |
|---|---|
| Applies to | all elements |
| Inherited | yes |
| Computed value | as specified with variables substituted |
| Animation type | discrete |
Syntax
--some-keyword: left;
--some-color: #123456;
--some-complex-value: 3px 6px rgb(20 32 54);
<declaration-value>-
This value matches any sequence of one or more tokens, so long as the sequence does not contain any disallowed token. It represents the entirety of what a valid declaration can have as its value.
Note:
Custom property names are case sensitive ā --my-color will be treated as a separate custom property to --My-color.
Example
HTML
<p id="firstParagraph">
This paragraph should have a blue background and yellow text.
</p>
<p id="secondParagraph">
This paragraph should have a yellow background and blue text.
</p>
<div id="container">
<p id="thirdParagraph">
This paragraph should have a green background and yellow text.
</p>
</div>
CSS
:root {
--first-color: #1166ff;
--second-color: #ffff77;
}
#firstParagraph {
background-color: var(--first-color);
color: var(--second-color);
}
#secondParagraph {
background-color: var(--second-color);
color: var(--first-color);
}
#container {
--first-color: #229900;
}
#thirdParagraph {
background-color: var(--first-color);
color: var(--second-color);
}
Result
Specifications
| Specification |
|---|
| CSS Custom Properties for Cascading Variables Module Level 1 # defining-variables |
Browser compatibility
See also
- The
var()function @propertyat-rule- Using CSS custom properties (variables) guide
- CSS custom properties for cascading variables module