css/cssom/getComputedStyle-root-variables.html

<!DOCTYPE html>
<meta charset="utf-8">
<title>getComputedStyle with CSS variables on :root</title>
<link rel="help" href="https://drafts.csswg.org/css-variables-1/">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<!-- Regression test for https://github.com/jsdom/jsdom/issues/3563 -->

<style>
  :root { --test-var: red; }
</style>

<body>

<script>
"use strict";

test(() => {
  const computedStyles = window.getComputedStyle(document.body);
  assert_equals(computedStyles.getPropertyValue("--test-var"), "red");
}, "getComputedStyle should return CSS variables defined on :root");
</script>