LayoutTests/imported/w3c/web-platform-tests/shadow-dom/focus/focus-pseudo-on-shadow-host-1.html

<!DOCTYPE html>
<html>
<head>
<meta name="author" title="Ryosuke Niwa" href="mailto:rniwa@webkit.org">
<meta name="assert" content=":focus should match a shadow host which contains the focused element">
<link rel="help" href="https://html.spec.whatwg.org/#element-has-the-focus">
<link rel="help=" href="https://bugs.webkit.org/show_bug.cgi?id=202432">
<link rel="match" href="/css/reference/ref-filled-green-100px-square.xht">
</head>
<body>
<p>Test passes if there is a filled green square and <strong>no red</strong>.</p>
<div id="host"></div>
<style>
#host { background: red; width: 100px; height: 100px; }
#host:focus { background: green; }
</style>
<script>

const shadowRoot = host.attachShadow({mode: 'closed'});
shadowRoot.innerHTML = '<div tabindex="0" style="outline: none;"></div>';
shadowRoot.firstChild.focus();

</script>
</body>
</html>