It seems that once you change one of the settings in the global project font settings, you can’t go back.
For example: I set the font setting for"All" to Roboto 16px in red. Now if I take a look at the font setting for “navigation links” it is set to inherited - which means it uses the font I set up under “All”.
I now open the project settings and change the font for “navigation links” to Ubuntu 17px Bold.
I change my mind and decide I want to go back to using the “default” font (defined for the body by using the “all” setting).
It seems this is not possible. Am I missing something here?