Definitely, yes. CSS (just as HTML, JS, and anything else being served) is covered by copyright. The law(s) may vary depending on jurisdiction, but generally speaking you can be sued for copyright violation. Getting caught is a different matter, but if it is obvious that you copied CSS you can be in serious legal trouble.
if i replaced just the logo in the upper left hand corner to the github logo instead of the googs logo would you be able to tell the difference between this screenshot and github proper?
> if i replaced just the logo in the upper left hand corner to the github logo instead of the googs logo would you be able to tell the difference between this screenshot and github proper?
I think I could easily do that.
And I'm a backender-at-heart who doesn't even have full colour vision.