css/css-scoping/host-nested-001.html

<!doctype html>
<title>CSS Test: :host doesn't match nested shadow hosts.</title>
<link rel="author" title="Emilio Cobos Álvarez" href="mailto:emilio@crisal.io">
<link rel="help" href="https://drafts.csswg.org/css-scoping/#host-selector">
<link rel="match" href="reference/green-box.html">
<style>
  #host {
    width: 100px;
    height: 100px;
  }
</style>
<p>Test passes if you see a single 100px by 100px green box below.</p>
<div id="host">FAIL</div>
<script>
  let root = host.attachShadow({ mode: "open" });
  root.innerHTML = `
    <style>
      div {
        background: green;
        width: 100px;
        height: 100px;
      }
      :host { background: red !important }
      div:host { background: red !important }
    </style>
    <div id="nested-host">FAIL - nested shadow host</div>
  `;
  root.getElementById("nested-host").attachShadow({ mode: "open" });
</script>