No problem, and no need to apoligise, CSS is certainly tricky on it's own and themeing Moodle adds a bunch of interesting twists.
Iteresting that you ask about documentation, as a space for this kind of small theme hint already exists:
http://docs.moodle.org/en/Theme_scrapbook
The docs wiki is only new (3 month old or so) but growing quickly and I intend to add this hint, and all the bits I've created for the Kubrick theme (which is basically mostly a collection of little workarounds and ideas) into this area, and help Urs (who has done pretty much all the CSS documentation you can find in the forums and Docs wiki) to pad it out with more even info.
On that note, if you find any areas where the image still shows through or any other problems with CSS documentation, please report bugs/problems to this forum and add suggestions/alternatives/tips to the wiki where appropriate.
(There's an index of Theme related documentation in the wiki here: http://docs.moodle.org/en/Category:Themes)