<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN">
<html>
<head>
<style>
.green {
  width: 100px;
  height: 100px;
  background-color: green;
}

.red {
  width: 100px;
  height: 100px;
  background-color: red;
  margin-top:100px;
}

.overflow {
  overflow: hidden;
}
</style>
<body>
You should see a 100x100 green square below.  If you see any red, the test
has failed.

<div class="green overflow"><div class="red"></div></div>