Newbie assigned to support and change OJS site seeks assistance

Hello: I have been assigned to support an OJS site at our University:
I’m being asked to make certain adjustments to the colors and spacing on the site. I’ve worked as a programmer and librarian, but am not (yet) a web programmer. Looks like (initially) that I might need to edit one or more .css files. How should I best post questions and make best initial use of this forum? And, are there any other useful OJS forums that I should be aware of? Thanks for any pearls of wisdom anyone might have to get me started in the most efficient way(s).

You should check these guides:

I am not aware of any other OJS forum, but development discussions you can find in Github: Issues · pkp/pkp-lib · GitHub

And of course there is the wiki, but it does contain some outdated information: