Anyone who has spent much time working with Cascading Style Sheets (CSS) has discovered that each browser has slightly different support for the various CSS versions.  To further complicate CSS usage, each browser has a different set of bugs and/or understanding of what a particular standard requires.  Internet Explorer is definitely the worst offender and the furthest from fully and faithfully supporting CSS 2.1.  While support has been steadily improving between versions, it is still not on par with other modern browsers.

Typically, designers use a number of different hacks to target CSS at specific browsers in order to work around the inconsistencies.  The process generally starts with a skin design which renders correctly in Firefox and then the designer adds hacks to get it to work in IE.  To make matters worse, Microsoft has made changes in each subsequent version of IE such that a hack that worked in IE5.5 will not necessarily work in IE7. More...