You should really check out this stylesheet demo site. It renders boxes properly with Netscape 4.5 in WinNT. I also recommend trying different browsers against the W3C CCS Test Suite if you want to know what they can do, it's a great reality check when something you coded doesn't show up right. Western Civ has some interesting if semi-ugly pages with a great browser compatibility matrix. They also have other good stuff nearby. Since imperfect HTML can get really hosed by stylesheets, validate your html. If you use CGI.pm, watch out--it generates a HTML 2.0 doctype descriptor that this validator hates (is this a bug?). You may also want to validate your stylesheet. I hope you find this info useful, even though it ain't strictly Perl.

Update: The newest versions of CGI.pm can generate a variety of doctype declarations.