Publisher writes it's own CSS. There is no support for a custom CSS file.
You would need to use a web design tool for that functionality.
You cannot compare a slide show program like PPT to a desktop publishing
program like Publisher. Nor can you compare a slide show runtime executable
file to a web site.
That said, there are some "page" level design options available in the IE
browser (nothing that should be compared to a slide show program) that
provide various "effects". Refer to
http://msdn.microsoft.com/library/default.asp?url=/workshop/author/filter/filters.asp
Such functionality would be out of Publisher's design scope. You'd want to
move to a web design tool, i.e. FrontPage.
David Bartosik - [MSFT MVP]
www.publishermvps.com
www.davidbartosik.com