host-with-default-namespace-001.html

<!doctype html>
<meta charset="utf-8">
<title>CSS Test: :host ignores default namespace</title>
<link rel="author" title="Emilio Cobos Álvarez" href="mailto:[email protected]">
<link rel="help" href="https://drafts.csswg.org/css-scoping/#host-element-in-tree">
<link rel="help" href="https://drafts.csswg.org/selectors-4/#featureless">
<link rel="help" href="https://bugzil.la/1546375">
<link rel="match" href="reference/green-box.html">
<p>Test passes if you see a single 100px by 100px green box below.</p>
<div id="host"></div>
<script>
  document.getElementById("host").attachShadow({ mode: "open" }).innerHTML = `
    <style>
      @namespace url(http://www.w3.org/2000/svg);
      :host { background-color: green; width: 100px; height: 100px; }
    </style>
  `;
</script>

chromium/third_party/blink/web_tests/external/wpt/css/css-scoping/host-with-default-namespace-001.html