Possible Duplicate:
Cross-browser CSS
Ok, so the question might be somehow a little confusing. I'm gonna try to put it in a much simpler way so "you" can understand my point of view.
All browsers are different. Every browser interprets the CSS rules diferent, which drives to different results. Some times the results are good other times and much often results are totaly unexpected. The case of IE can lead to the worst scenario possible!
Many often, developers are forced to detect the browser to apply a specific css style! This can be achieved with javascript support. Anyhow, some people say that this method it's not enough to prevent disasters... others think that the best way to deal with this problem it's to rely on Object detection instead.
Well, I don't know which one is best... Please feel free to give you opinion based on examples. As always, thank you.
UPDATE
The case of IE can be very simple to deal with conditional statments but, safari can't be treated the same way! So I leave this link: http://quirksmode.org/js/support.html to clarify my point of view...