My question is how do you learn to design any application?
Some people naturally develop the ability to create beautiful things, even if they are not always very usable. The rest of us have to learn it by exposing ourselves to good design and understanding what makes things pleasant to look at and easy to use.
I think something like Refactoring UI by Adam Wathan and Steve Schoger, the creators of Tailwind CSS, is probably what you are looking for. It offers very practical guidelines and recipes for creating beautiful user interfaces.
For learning about UX, I’ve heard great things about the following books, although they might be a bit dense depending on what you are after:
Disclaimer: I am not a designer.