When using CSS in you web page, the CSS looks always want you to give out the exactly height and width  to each of the block in you pages. But in a dynamic web site, the content is loaded from database and can be updated by user again and again,  we will never know what the content's width and height will be.  So control the block's height change don't break the page's view are a very important task for a web developer.

and another challenge thing  is make you page looks always good in different browsers.

The worse thing is if  your css  didn't define some of  values, it will looks different in different browsers, see below image, my test page have different look in IE6,Firefox, and Chrome:

To fix it is very simple, just need add one line in the Css for the parent block

overflow:auto;

Some discussions are here http://bbs.et8.net/bbs/showthread.php?t=973769