This is something I have been looking for as well. Unfortunately, there is no such utility (that I have found) to convert HTML to PDF with CSS support. Here are the utilities that I have come across that you may be interested in:

HTMLDoc - Provides a free version (which you must compile form source or find a binary on the internet, which the provide links to) and a commercial version. Provides basic HTML support (no CSS), with some limitations (for instance - try using tables within tables to layout your pages). There is a corresponding perl module to interact with HTMLDoc.

html2ps - Converts html to postscript - not sure if supports conversion to pdf as well.

A possible alternative is to use the Gtk2::MozEmbed to render the html and print to then print to PDF. I was not able to get Gtk2::MozEmbed to work on windows (if anybody has, please contact me).