<html>
  <style>
    #green {
      background-color: green;
      margin-bottom: 50px;
    }
    #red {
      background-color: red;
      margin-bottom: 50px;
      border-bottom: 10px solid blue;
      width: 50px;
      height: 50px;
    }
    #yellow {
      background-color: yellow;
      width: 50px;
      height: 50px;
    }
  </style>
  <body>
    <div id=green>
    	<div id=red></div>
    </div>
    <div id=yellow></div>
  </body>
</html>