If I´m correct that´s the number Nigel has right?... He´ll give you an answer, but I can guess a couple of things:
a) There are in fact two CSS styles when you look them with Fire Fox. The first one is the "standar" Pbase (called Gallery2.css or something like that) and the other one, that should have a number like the one you described. That´s the one you can modify.
Do you reference one of them as one of your style sheets and the other in the description file?
b) Therefore, that´s the one you work on. If by "reference" you mean select your personal style sheet in the edit page of the gallery you are right. But that´s not done in the description field... I´m not sure if I understand you correctly, so I´m telling this just in case there is a confusion about how to select a stylesheet.
c) Last advice: There are a lot of guys (like me) that have personal style sheets. Some are cool, but the problem is that they are not "correct"; some have code problems, some have extra "classes" from the original pages from they where taken in the first place, etc... So It would be a good idea to use the stylesheets from the guys that like to use Validation Forms, like Nigel, Rob, Arjun, Alan, Webdev.... It is already hard to understand all the codes, it is even harder to understand what is wrong if you don´t even understand them!
Hope this helps you - Take care