You only need to save the files that you need.
I recommend checking out the screenshots in Styles & Screenshots (post 61) before saving antying, to see which style you’d like and to understand which files you will actually need.
If you like the fenix style, you can simply save fenix_one.css as userChrome.css and then save one of the userContent.css files, and that’s it. Two files for everything. If you want bigger popups, you can simply copy/paste one of the dynamic_popups files to the bottom of the userChrome.css file.
Feel free to ask questions if you need any help.