<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN">
<html lang="en">
 <head>
  <title>Margin Collapsing: negative margins (easy)</title>
  <style type="text/css">
   .container { background: red; height: auto; border: 1em lime solid; }
   .a { margin-top: 1em; margin-bottom: 1em; }
   .b { margin-top: 1em; margin-bottom: 1em; }
   .c { margin-top: 1em; margin-bottom: 1em; }
   .d { margin-top: 1em; margin-bottom: 1em; }
   .e { margin-top: 1em; margin-bottom: -1em; }
   .f { margin-top: 1em; margin-bottom: 1em; }
  </style>
 </head>
 <body>
  <p>There should be no red below.</p>
  <div class="container">
   <div class="a">
    <div class="b"> </div>
    <div class="c"> </div>
   </div>
   <div class="d">
    <div class="e"> </div>
    <div class="f"> </div>
   </div>
  </div>
 </body>
</html>