The wiki’s CSS affects the experience for every user in the wiki, and can only be edited to by Admins.

Your personal CSS only effects your experience and can only be edited to by you

Thank you.

What Bladdest said. It's also important to note that some scripts can only be on your personal CSS due to violating the Customization policy if they're wiki-wide.

I just wish to test out my username colors on the WoF wiki for the WCFW wiki