Most Themes: Change font size of primary menu only

This Code Hack is compatible with the Barton, Hayes, Pearl, Rania and Presidio themes.

Depending on your theme, available Customizer controls, and your customization preferences, some users may wish to change the font size of the Primary Menu. This is the menu that is placed underneath your site logo/title, or inline with it. (For more on our theme menus, click here.)

Here is what this Code Hack looks like in action:

And here is the code you need to implement it!