Custom properties (--*): CSS variables - CSS: Cascading Style Sheets 编辑

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.

Syntax

--somekeyword: left;
--somecolor: #0000ff;
--somecomplexvalue: 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 an unallowed token. It represents the entirety of what a valid declaration can have as its value.

Note: Custom property names are case sensitive — --my-color will be treated as a separate custom property to --My-color.

Formal syntax

<declaration-value>

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: #16f;
  --second-color: #ff7;
}

#firstParagraph {
  background-color: var(--first-color);
  color: var(--second-color);
}

#secondParagraph {
  background-color: var(--second-color);
  color: var(--first-color);
}

#container {
  --first-color: #290;
}

#thirdParagraph {
  background-color: var(--first-color);
  color: var(--second-color);
}

Result

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• Using CSS variables
• The var() function