Text size for navigation bar should be same, bigger or smaller than 16px?

The default font size is 16px, but I don't know if the font size of the navigation menu should be the same (16px), smaller (14px) or bigger than 16px. I think that bigger than 16px is going to be complicated because I could not add many elements and I must add a login button and another one that will have three words. Also, the language selector.

Are there any rules or best practices about this?