Maybe you can add some sort of “vignette” or a gradient to tint the corners/part of the screen and make the GUI look less “Empty”. You can also try to add some light in front or behind the diamond to add shading and make it look less flat. You could also add a circle around the diamond (like some sort of frame).
Also, don’t forget to maintain the artstyle of your game in your GUIs as well (it looks better and more “AAA”).
Hope it helps
What I meant by it is that you should make your GUI’s colors/textures look similar to the ones you use in the game (example : if you make a steampunk styled game don’t use futuristic fonts/colors, etc…).
Let me know if I am clear enough