@GreenChocho That’s very odd, there’s no part of it that changes colours or affects anything like that - it should be completely theme-proof. I’ve just installed gruvbox and tested it, and I can’t recreate your issue at all. The only thing I can suggest is switching to another theme and checking that the hover behavior works, and then switching back to gruvbox (turn it off, turn it back on…)
Or maybe try pasting the code above into your snippet file again. If you didn’t get all of it (missing brace or something) then I guess it could interfere with the theme loading (can’t really see how, but you never know).