shadow-link-rel-stylesheet-no-style-leak.html

<!doctype html>
<title>CSS Test: &lt;link rel="stylesheet"&gt; in Shadow DOM doesn't affect the normal DOM</title>
<link rel="help" href="https://html.spec.whatwg.org/#link-type-stylesheet">
<link rel="help" href="https://drafts.csswg.org/css-scoping/#selectors-data-model">
<link rel="match" href="reference/green-box.html">
<p>Test passes if you see a single 100px by 100px green box below.</p>
<style>
  #light-dom {
    width: 100px;
    height: 100px;
    background: green;
    color: green;
  }
</style>
<div id="host">FAIL</div>
<div id="light-dom"></div>
<script>
  host.attachShadow({ mode: "open" }).innerHTML = `
    <link rel="stylesheet" href="data:text/css,div { background: red !important }">
  `;
</script>

chromium/third_party/blink/web_tests/external/wpt/css/css-scoping/shadow-link-rel-stylesheet-no-style-leak.html