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Custom properties (--*): CSS variables

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 {{cssxref("var", "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 any disallowed 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.

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​

{{EmbedLiveSample('Example', 500, 130)}}

Specifications​

Browser compatibility​

See also​