Trouble in Terrorist Town menu has missing textures, can't click controller in the main menu.

Hi guys, please note that I am new to Garry’s Mod and a bit of a noob.
Okay, so I’ve been playing Gmod a while now and I just recently started playing TTT. When I join a game everything is fine and the guns and world textures don’t have any problems. However, if I open the traitor menu ( c ) or investigate a body there are black and purple checkers all over the area. I have CSS and people are saying that you need to enable it in the main menu through the little controller in the right corner. When I click that button my mouse stays as if it were hovering over it and no menu pops up. I am running Ubuntu Linux. Any help would be great, thanks in advance. If you need any info just say so.