When the tab reads 'dark', you're using the light scheme, and vice versa. If you want it dark, you need to press the 'dark' tab, afterwards it reads 'light'.
The default setting doesn't have dark or light tabs, it's always light. To get a dark and light variant, you need to use the Lapis Watch or Amber Watch schemes.
I'm doing so now and everything looks fine (Opera 9.02). Lapis and Amber should only be different colors, really, nothing else. Are you using an older version? Or maybe try to shift-click the reload button, in case some wrong data has been cached.BTW, Lapis dark does'nt display properly using Opera, but Amber dark(sounds like a beer ) is fine. I can't explain how Lapis dark displays on Opera, you'll just have to see for yourself.
I doubt this is a site issue, but I've noticed something strange. When I first visited this site the first thing I noticed was that everything was really huge. For example, this "Quick Reply" window is taking up about half of my LCD widescreen 24" screen.!