chromium/third_party/blink/web_tests/external/wpt/css/css-counter-styles/counter-style-at-rule/shadow-dom-part.html

<!DOCTYPE html>
<title>Counter style tree-scoped references</title>
<link rel="help" href="https://drafts.csswg.org/css-counter-styles-3/#the-counter-style-rule">
<link rel="help" href="https://drafts.csswg.org/css-scoping/#shadow-names">
<link rel="author" href="mailto:[email protected]">
<link rel="match" href="shadow-dom-part-ref.html">
<meta name="assert" content="The list in the shadow tree should use the counter style defined in the outer document, because it's styled by the outer document">

<style>
@counter-style foo {
  system: fixed;
  symbols: A B C;
}
#host::part(list) {
  list-style-type: foo;
}
</style>

<div id="host"></div>

<script>
document.getElementById("host").attachShadow({mode: 'open'}).innerHTML = `
<style>
@counter-style foo {
  system: fixed;
  symbols: D E F;
}
</style>
<ol part="list" style="list-style-position: inside">
  <li></li>
  <li></li>
  <li></li>
</ol>
`;
</script>