<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN">
<html lang="en">
 <head>
  <title>Margin Collapsing: floats</title>
  <style type="text/css">
   div.test { background: green; float: left; }
   div.test div { background: red; margin: 5em 2.5em; }
   div.control { height: 5em; width: 5em; margin: 0 0 -5em 0; background: red; }
  </style>
 </head>
 <body>
  <p>This page should have one square green block and no red.</p>
  <div class="control"></div>
  <div class="test">
   <div></div>
  </div>
 </body>
</html>