What kind of choices do Apple provide for fonts and styles? Sorry if thats a very broad question. I'm trying to work out how the Nike app looks brilliant (but goes like a cow on a bike...), but all the other apps appear to look very similar (although tend to work significantly better than NRC).
Do you mean in terms of the force touch menu or more generally?
If you mean in terms of the force press menu, then apps can control the icon in terms of its shape but it must be black & white. The font size and style is fixed. Apple also provide standard icons for a lot of operations, such as pause and resume, so it is best to use them if available for the operations in menu.
If you mean more generally then apps have a lot of control over fonts and styles. I guess that Nike either have graphic designers dedicated to how the app looks, or their coders are more artistically talented than the rest of us (which is not difficult in my case)!