My GFX skills are very little and I havent done something like this for 10 years or so 
So this wasnt a try to make a own UI Theme, i cant do that 
I just reduced the colors and shiny buttens a little bit for myself to concentrate better on the actual gameplay and thought maybe someone might be interested in the files as well.
But i take ur advice and keep playing with it around, maybe i figure out how to make my own buttons etc xd
Here is a Link to the Files, i will keep it updated as i make progress: