chromium/third_party/blink/web_tests/external/wpt/webvtt/rendering/cues-with-video/processing-model/selectors/cue/cue_selector_single_colon.html

<!DOCTYPE html>
<html class="reftest-wait">
<title>WebVTT rendering, :cue (single colon) should not be supported</title>
<link rel="match" href="cue_selector_single_colon-ref.html">
<style>
html { overflow:hidden }
body { margin:0 }
:cue {
    background: red;
    color: yellow
}
</style>
<script src="/common/reftest-wait.js"></script>
<video width="320" height="180" autoplay onplaying="this.onplaying = null; this.pause(); takeScreenshot();">
    <source src="/media/white.webm" type="video/webm">
    <source src="/media/white.mp4" type="video/mp4">
    <track src="../../support/test.vtt">
    <script>
    document.getElementsByTagName('track')[0].track.mode = 'showing';
    </script>
</video>
</html>