hello there, 

I would like to change the menu font size of the main menu that shows up full screen  when opening the "sandwich" icon top right. 

I found a place under THEME OPTIONS > HEADER OPTIONS > MENU FONT SIZE > and chose SMALL  here ... but it doesnt seem to affect the menu. I am asuming this must be refering to a different set-up of menu?

( I add screenshots to expain which menu and hwere I am tryign to modify it in the admin)

Where would I have to look?  Or is this a custom css?

It is not that I was not happy with the pre-sets that were available for the menu - they just didnt seem to work for me . 

Changing between big and small didnt show any difference .

In any case, the code you send me worked well. Thank you!!