Are they possible?
they should be I think my brother has some for half life, but I’m not sure.
I think he means HUDs, but not sure.
I think he might mean backgrounds.
There is a difference. Backgrounds just affect the image at the back (for example, changing the current GMod background for a picture of the heavy), whereas themes affects buttons as well (like getting a new theme for a computer will change the taskbar thing at the bottom).
Therefore, I don’t think that themes are possible for GMod, without extensive Lua coding.
So do you mean Themes =/= Backgrounds?
Yes, there are not same thing and no, they are the same thing. See, themes add buttons and backgrounds, where as backgrounds just add err… backgrounds.
You can use backgrounds for any Source game on GMod, visit FPSBanana and have fun.