In the latest version, a shadow was added to the action bar, which completely destroyed the possibility of creating a custom user interface. On the example of the "thirst" datapack, we see how this affects the appearance. It is the absence of a shadow that makes it possible to create beautiful interfaces. My suggestion is to add a special "shadow" tag to be able to disable or enable the shadow.

Before 1.19.1: 

After 1.19.1:

Need new tag>   {"text":"dontshadow","color":"white","shadow":"false"}