css/css-cascade/layer-slotted-rule.html

<!DOCTYPE html>
<title>::slotted rules should be associated with the correct cascade layers</title>
<link rel="help" href="https://drafts.csswg.org/css-cascade-5/#layering">
<link rel="author" href="mailto:xiaochengh@chromium.org">
<link rel="match" href="reference/ref-filled-green-100px-square.xht">
<style>
#target {
  width: 100px;
  height: 100px;
}
</style>

<p>Test passes if there is a filled green square and <strong>no red</strong>.</p>
<div id="host">
  <div id="target"></target>
</div>

<script>
const host = document.getElementById('host');
host.attachShadow({mode: 'open'}).innerHTML = `
<style>
@layer {
  ::slotted(*) {
    background-color: green !important;
  }
}
::slotted(*) {
  background-color: red !important;
}
</style>
<slot></slot>
`;
</script>