shadow-host-removal-invalidation.html

<!doctype html>
<title>CSS Test: Invalidation of :host selectors</title>
<link rel="author" title="Emilio Cobos Álvarez" href="mailto:[email protected]">
<link rel="author" title="Mozilla" href="https://mozilla.org">
<link rel="help" href="https://drafts.csswg.org/css-scoping/#host-selector">
<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1499603">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<div id="host" style="color: green"></div>
<script>
host.attachShadow({ mode: "open" }).innerHTML = `
  <style>
    :host { color: red !important }
  </style>
`;
test(function() {
  assert_equals(getComputedStyle(host).color, "rgb(255, 0, 0)");
  host.shadowRoot.querySelector("style").remove();
  assert_equals(getComputedStyle(host).color, "rgb(0, 128, 0)");
}, ":host rules are properly invalidated when stylesheets are removed");
</script>

chromium/third_party/blink/web_tests/external/wpt/css/css-scoping/shadow-host-removal-invalidation.html