css/css-variables/variable-declaration-29.html

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<!DOCTYPE html>
<title>CSS Test: Test declaring a variable with an invalid custom property name "--".</title>
<link rel="author" title="Cameron McCormack" href="mailto:cam@mcc.id.au">
<link rel="help" href="http://www.w3.org/TR/css-variables-1/#defining-variables">
<link rel="match" href="support/color-green-ref.html">
<style>
p {
  color: green;
  --: red;
  color: var(--,crimson);
}
</style>
<p>This text must be green.</p>