Okay… so that part of the docs is overdue for an update. We had talked about having a defined set of “defaults” that every theme should adhere to. These are generally what is set up in the standard Tailwind themes. See Font Size, Theme Spacing, Shadows, etc. Font Family is a little different.
The control will attempt to select what you put as a default, but if it’s not available, it should just pick the first value. So nothing will “break”.
We plan to provide a guide on creating custom themes and the required defaults. I’m now thinking we should do this sooner, rather than later 
As long as you’re using the theme UI controls, your components will work much better and get all the improvements we make 
Sorry for the rambling answer, feel free to follow-up with more questions!