With update 2.0.0 this mod uses a texture sheet so you can freely replace or paint your own assets. The tutorial below will detail the steps you need to take to use it properly.

HOW TO USE THE TEXTURE SHEET:
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1. Open the texture sheet
The texture sheet is inside the textures\gui folder

2. Paint Your Design
Open this image in your preferred digital art software (Aseprite, Photoshop, etc.). Draw your custom design anywhere on the transparent canvas. 
Note: Keep the background transparent, and save it as a standard .png

3. Find Your Coordinates (UV Mapping)
For the mod to read your texture properly, it needs to know exactly where on the sheet your drawing is, and how big it is. You will need four numbers:
  - Starting X: The X-coordinate of the very top-left pixel of your drawing. ( u )
  - Starting Y: The Y-coordinate of the very top-left pixel of your drawing. ( v )
  - Width: How many pixels wide your drawing is. ( w )
  - Height: How many pixels tall your drawing is. ( h )
Note: Change the 4 numbers for the item you are replacing for example if you are replacing the bonus separator then you chang ethe 4 numbers for bonus separator, not add a new one.

And thats it!

For regen indicators it has an extra step below

4. Update Your Config
Launch the game (or edit your client.toml file directly) and navigate to the Stamina config UI settings.
  - Set "Regen Indicator Style" to CUSTOM.


Also note that this is my first time doing this so expect some bugs (even though I tested it relatively thoroughly), in the case you find some bugs let me know on github or in comments and I will take a look and see what I can do.