<html>
<head>
<style>
div.box {
  height: 100px;
  background-color:green;
  display: -moz-box;
  display: -khtml-box;
  display: box;
  width: 100%;
}

div.innerBox {
  background-color:red;
  height:100px;
}
</style>
</head>
<body>
You should see a green rectangle below that is 100 pixels tall and that fills the width of the content area.  If you see any red, then the test has failed.  

<div style="background-color:red;height:100px">
<div class="box">
<div class="innerbox"></div>
</div>
</div>
</div>
</body>
</html>