Unless you are having to support Netscape 4, CSS should be identical for all browsers. Since older browsers constitute less than 1% of the traffic to my sites, I've forgotten all about the browser wars.

It sounds like you are being asked to do this from above. Now would be a very good idea to suggest some of the strategies put forward by Jeffrey Zeldman on designing with web standards.

If you are using HTML as a machine-readable data format, how will any presentational style information be used?