How to set Themename in fullcalendar?

To set themeSystem in Fullcalendar you use:

themeSystem: 'bootstrap4',

But how do i set themeName ?
Does it even exist?

Take a look at this page:
https://fullcalendar.io/releases/fullcalendar/3.10.0/demos/themes.html

Here you can choose both Theme system & Theme name!

I've tried: themeName: 'Lumen'