[CarlitoBrigante]

There is now a hook for the original purpose of this thread. As I said, this thread can now be considered obsolete. Now it has become as easy as creating a "yourcss.css" template, adding a plugin in the parse_template hook, and then do something like this in the plugin:

$template_hook['custom_css_list'] .= ',yourcss.css';

This thread was made for product creators that needed a simple way to attach css to their styles with no need for people installing their stuff to edit their templates.