Looks great. Only 2 recommendations
1) Perhaps use a thicker font, or different font color for the Panel Titles? (Menu, Login Screen, Inventory)
The thin font combined with black letters on a dark red background makes it hard to read.
2) Borders of some kind on the action bar slots?
Otherwise, looking great! IHopefully when I make my UI I can create something that looks this nice.
Also, that health bar looks really good. Simple, but very good.