While it's indeed a little long, it's pretty organized, and I also don't see many things that could be defined as "outdated". Of course, some of it may be unnecessary but indeed there's no simple method for checking where a certain selector is used around the site. I'm not saying there aren't methods at all, but any method I can thing about would require some tampering and I'm not sure it's worth it for ~1000 lines of CSS. In my opinion it's quite reasonable to leave it as it is.

Yes, it is at least organized but if all goes well a bunch of new CSS will be added, some table designs are being completely scrapped and I just was hoping to give them a cleaner and more organized version but some of the CSS there I haven't the foggiest if it is even still being used.

I think I might just on my personal wiki alter the same fields with outrageous values and see if during regular editing and browsing if the CSS styles comes up. Unless you have any better tampering methods?

I don't think that's going to work. Most of the CSS rules are applied to custom selectors that may be used on any random page around the wiki, so unless you visit that particular page you would see nothing different, even less if you are browsing another wiki.

I am currently heavily involved with this wiki atm, one of my tasks is updating all the pages that still have CSS from before there was dark mode, and the tables are unreadable in dark mode. I have already during the summer managed to check at least for the unreadable dark mode tables articles from A-L. I'd not be able to be 100% sure but it is a thought.

Sure, if you know where to look, if you know the wiki, the templates, the tables etc. - that's a lot easier. If you need to ask what a particular CSS rule means in order to nail it down - you're welcome to ask.

I just mean that you can't this way confirm it's not used "somewhere".

Yeah, I can do that :)

Also, I just tried my method and immediate found something and updated accordingly. I already mentioned to one of the bureaucrats (we should/might apply a major theme overhaul of the wiki) that we might want to have a live beta testing period so feedback and issues can be posted, I just thought, while we are at it lets see if we can trim the fat on the other CSS too, while people are knowingly aware of the transition and posting issues if any.

"I'm not saying there aren't methods at all"

While it would still be quite a task in this case here to search for hundreds of selectors, I really wish the MassEdit script had an option to search & report only. That script can go through every (or certain) page(s) and replace anything with something else, while also returning a log-line (found/not found) for each page searched. I feel it should be very easy to add an option that does the exact same just without the replacing part. This would be sooo helpful sometimes if you just want to find some words or phrases or pattern without replacing anything.

This was actually requested earlier this year already by someone on its talk page, but nobody ever answered.