<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"> <html> <head> <style> .green { width: 100px; height: 100px; background-color: green; left: 100px; top: 70px; } .red { width: 100px; height: 100px; margin-top: 100px; margin-left: 100px; background-color: red; } .overflow { overflow: hidden; width: 100px; height: 100px; } .positioned { position: fixed; } </style> <body> You should see a 100x100 green square below. If you see nothing at all or see any red, the test has failed. This test is checking to make sure overflow is done using a containing block model, and that a fixed positioned element inside another fixed positioned element is not considered overflow. <div class="overflow positioned"> <div class="red"></div> <div class="green positioned"></div> </div>