There isn't anything that's up to date; this is on the todo list. Some CSS-related revamping is planned for Tiki 7, so this will be a good opportunity for detailed overviews both for that version and for Tiki 6, which is the new long-term support version.
For a more immediate solution, you can use Firefox and the Firebug add-on (there are other similar tools for IE and Opera, etc.) to check the CSS selectors used in a page with your browser.
About the "minitemplates," this is a good idea that coincides with some things I was thinking, about having more "how to" documentation on Tiki layouts, such as within a wiki page to make a portal-like "page of boxes" etc. In general it would be about how to take the next steps after Tiki is installed and functioning as desired, regarding site layout and appearance. I think this will also dovetail with the pre-Tiki 7 CSS rejiggering. I'll make a wiki page here about it when things firm up a little more.