css/css-scoping/shadow-assign-dynamic-001.html

<!doctype html>
<meta charset="utf-8">
<title>CSS Scoping Module Level 1 - Dynamic mutations to both shadow root and shadow host subtrees</title>
<link rel="author" title="Emilio Cobos Álvarez" href="mailto:emilio@crisal.io">
<link rel="help" href="https://drafts.csswg.org/css-scoping/#selectors-data-model">
<link rel="help" href="https://bugzil.la/1303605">
<link rel="match" href="reference/green-box.html"/>
<p>Test passes if you see a single 100px by 100px green box below.</p>
<style>
  #host {
    width: 100px;
    height: 100px;
    background: red;
  }

  #host > div {
    width: 100px;
    height: 50px;
    background: green;
  }
</style>
<div id="host"></div>
<script>
  let root = host.attachShadow({ mode: "open" });
  document.body.offsetTop;

  root.innerHTML = `<slot name="slot1"></slot><slot name="slot2"></slot>`;
  host.innerHTML = `<div slot="slot1"></div><div slot="slot2"></div>`;
</script>