<!doctype html>
<html>
<body>
    <div style="width:0px; position:fixed">
      <div style="position:fixed; width:400px; height:400px; background-color:red"></div>
      <div style="left: 200px; top: 200px; position:fixed; width:400px; height:400px; background-color:blue"></div>
    </div>
<body>
</html>