chromium/third_party/blink/web_tests/compositing/geometry/video-opacity-overlay.html

<!DOCTYPE html>
<html>
<head>
  <style>
    video {
      width: 100%;
      height: 100%;
    }

    .container {
      position: relative;
      width: 400px;
      height: 300px;
      border: 1px solid black;
    }

    .controls {
      opacity: 0.8;
      height: 10px;
      width: 10px;
      background-color: green;
    }

    #control-bar {
      position: absolute;
      left: 0;
      bottom: 0px;
      width: 100%;
      height: 60px;
      background-color: orange;
    }
  </style>
  <script src="../resources/media-testing.js"></script>
  <script type="text/javascript" charset="utf-8">
    function testDone()
    {
      if (window.testRunner)
        testRunner.notifyDone();
    }

    function doTest()
    {
      var video = document.getElementsByTagName('video')[0];
      setupVideo(video, '../resources/video.ogv', testDone);
    }
  </script>
</head>
<body onload="doTest()">
  <p>The orange bar should be in front of the video.</p>
  <div class="container">
    <video></video>
    <div class="controls" id="controls">
      <div id="control-bar"></div>
    </div>
  </div>

</body>
</html>