Some browsers have problems properly rendering CSS. Notably, IE5 has some minor problems with div tags, color, and spacing. They are easily cleared up by scrolling the page all the way to the bottom then back to the top using the scroll bar, or by refreshing the page. Some of them also go away when I have valid HTML! ;)
Then there are other browsers, that know what CSS is, but don't properly support the customizations of tags (say, div.important, which then would be <div class="important" >). Sadly, this lack of support is worse than the afforementioned minor improper rendering. It results in very horrible rendering. If you are reading these pages with a CSS-capable browser, and the pages seem blank, or the text seems messed up, try using a browser that does a better job of rendering CSS
For more information on testing whether your browser properly supports CSS, use the W3C's tests designed for the very purpose.