This web site is about Cascading Style Sheets as a means to separate the presentation from the structural markup of a web site, and it will help you answer some of those frequently asked Questions, explains some of the Basics of CSS, gives you tips and tricks for tackling the problems with Netscape 4, offers you a tutorial about Positioning with CSS (CSS-P, web design without tables). There is also a page with interesting Links.
The market share of browsers that do not support any CSS is now below 0.5%. Therefore web developers have more freedom to actually separate content (HTML) and presentation (CSS).
The biggest challenges that web developers face when implementing CSS is backwards compatibility and browser support.
The problem is that most browser have been developed at a time when CSS was still in 'draft-mode' and by no means a web standard. Some browsers have been constantly updated since then, others not. Blooberry has a fascinating timeline for browsers and the history of CSS.
Today we have > 80% IE 5.0, 5.5 and IE6, less than 10% NN4.xx and approximately 3.5% IE4. Netscape 6, Opera and other browsers are fighting for the rest (http://www.upsdell.com/BrowserNews/stat.htm).
In short, sweet words: CSS1 support is at least partially available for more than 96% of the current browser population, with a good CSS2 support for about 80% of today's browsers.
In terms of backwards compatibility these numbers mean: we have some support for CSS since versions 4 - NN and IE. Unfortunately, NN 4.xx had only minor and cosmetic updates while Explorer was able to incorporate more CSS features, and re-work buggy implementations.
With the total rehash of Netscape 6 and Explorer 6 already released we can confidently look into the future, but in the meantime we have to live with a certain percentage of Netscape 4 browsers.
The issues that surface quite often in Newsgroups are: