css/css-pseudo/highlight-custom-properties-dynamic-001.html

<!DOCTYPE html>
<meta charset="UTF-8">
<title>CSS Pseudo Test: Dynamic Custom Properties for Highlights</title>
<link rel="help" href="https://drafts.csswg.org/css-pseudo/#highlight-styling">
<link rel="match" href="highlight-custom-properties-dynamic-001-ref.html">
<link rel="author" title="Stephen Chenney" href="mailto:schenney@igalia.com">
<meta name="assert" value="Custom property values in highlights update correctly when the property is updated.">
<head>
  <style>
    div {
      --background-color: red;
    }
    ::selection {
      background-color: var(--background-color, red);
    }
  </style>
</head>
<div id="originating">Green background when selected</div>
<script>
  window.getSelection().selectAllChildren(document.body);
  requestAnimationFrame(() => {
    requestAnimationFrame(() => {
      originating.style.setProperty("--background-color", "green");
      requestAnimationFrame(() => takeScreenshot());
    });
  });
</script>
</html>