can someone make SA2B site theme for entire site? pls?

You'd have to ask this to the site moderators or, if possible, apply this site theme to your own profile and then use that as a site theme. I don't know how that would work now, but I remember there used to be a way.

Edit: https://www.speedrun.com/the_site/thread/uow84 I provided an answer there, for those who are finding this thread. :)