<html> <head> <style> div.box { height: 100px; width: 100px; background-color:red; display: -moz-box; display: -khtml-box; display: box; } div.innerBox { width: 100px; background-color:green; } </style> </head> <body> <p>You should see a green 100x100 box below. If you see a red box, then the inner block is not properly growing to fill the height of the enclosing box. </p> <div class="box"> <div class="innerbox"></div> </div> </div> </body> </html>