<style>
.green {
  background: green;
  float: left;
  width: 100px;
  height: 100px;
}
.blue {
  background: blue;
  width: 200px;
}
</style>
<div class='green'></div><div class='blue'><br style="clear:both"><span></span></div>
PASS if blue box is as tall as the green one.