css/css-scoping/css-scoping-shadow-dynamic-remove-style-detached.html

<!doctype html>
<title>CSS Scoping: Invalidation of style data while ShadowRoot is disconnected.</title>
<link rel="author" title="Emilio Cobos Álvarez" href="mailto:emilio@crisal.io">
<link rel="author" title="Mozilla" href="https://mozilla.org">
<link rel="help" href="https://drafts.csswg.org/css-scoping">
<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1612114">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<div id="host"></div>
<script>
let t = async_test("Invalidation of style data while ShadowRoot is disconnected.");

let host = document.getElementById("host");
host.attachShadow({ mode: "open" }).innerHTML = `
  <style>
    div { color: red }
  </style>
  <div></div>
`;
assert_equals(getComputedStyle(host.shadowRoot.querySelector("div")).color, "rgb(255, 0, 0)");
host.remove();
host.shadowRoot.querySelector("style").remove();
requestAnimationFrame(t.step_func(function() {
  requestAnimationFrame(t.step_func_done(function() {
    document.body.appendChild(host);
    assert_not_equals(getComputedStyle(host.shadowRoot.querySelector("div")).color, "rgb(255, 0, 0)");
  }));
}));
</script>