<!DOCTYPE html>
<html>
<head>
  <title>video-with-alpha</title>
  <style>
    body {
        background: white;
    }

    #spacer {
        position: absolute;
        left: 200px;
        top: 0px;
        width: 200px;
        height: 200px;
        background-color: red;
    }
  </style>
 </head>
<body>
  <div id="spacer"></div>
</body>
</html>