The behind scene of the icon
The word "GUI" arranged in the container GUI is made by the Recovery Compasses that apply various item models.
This image shows how to get the item with a custom model via command, which gives you an item representing the top left part of the character "U" in the previous image.
Main Field pieces
Some pieces imitate container GUI and are named "main field".
The progress bars do have their progressing variants.
The extended slots, the right one have a "main field" background.
Sub Field pieces
Some pieces imitate the black field in the beacon GUI, named "sub field" compared to the "main field".
Buttons
The buttons for interaction use. (needs mod or data pack to achieve that function)
Demo 1
Reminder: The resource pack doesn't have the functionality to make this demonstration work.
Demo 2
Reminder: The resource pack doesn't have the functionality to make this demonstration work.
Demo 3
Reminder: The resource pack doesn't have the functionality to make this demonstration work.
Expansion demo
WARN: This demonstration shows assets not included in this resource pack. This one is from another project but uses similar parent files, its purpose here is to show how the concept can be expanded.