How make an UI / game layout something like this?

So I made a temporary test UI. It still lacks most of the fundamental components what make the use of such UI important for me,
but at least it demonstrates the style a bit for what I am aiming for.

It works now too, but I would LOVE to stop the game from rendering everything under the UI as it wont be visible anyway.
The framerate is better when I have a window of the same size open, than in the fullscreen where UI blocks everything.


There will be more things on the “UI” book and I will still adjust the sizes and framing of it as well, so it wont look as empty as it does now.