Bedrock GUI is pretty confusing but I’m assuming as you said, you have the default pack. If you do most of the GUI is in the GUI and UI folders I believe. If it’s possible I’d recommend trying to find a bedrock texture pack that says it only changes the GUI so you can use it somewhat as a template.
Yeh even tho I didn’t play Minecraft too much before the texture update, there’s something about programmer art that’s special. In general tho jappas textures look much better