Curious question
 

Could one add to UI, like a border to theme? I was really thinking about attempting a dark kinda theme, where screen would have a black spider web like border, I doubt i could pull of a nice one but it's idea I've had, i was wondering if it was possible. I'd like to be able to i guess instead of making everything invisible i'd like to give it a creepy theme :D :P yeah its kinda weird, but everyone has their interface quirks, and bright and shiny kills my eyes :(

At the moment you can't create new windows at all, so I'd say the answer would be "no", for now.

You can do this by reskinning the main silver boxes in the game. If you look at the current the blue or green mod - they show you how to make different borders.