host-pseudo-elements.html | Explore in Territory

<!DOCTYPE html>
<style>
  #host::after {
    content: 'After';
  }
</style>
<div id="host">Host</div>
<script>
host.attachShadow({ mode: 'open'}).innerHTML = '<span><slot></slot> ';
</script>

chromium/third_party/blink/web_tests/shadow-dom/host-pseudo-elements.html