Multiline menu with two font sizes

I’d like to make my top navigation menu have one regular line and then a second line (so two lines for each menu link)… but I want to make the second line of text slightly smaller than the top line. I’ve figured out how to make the two lines and do italics, which I don’t need, but I can’t figure out how to change the font size of the second line. Ideas?

Thanks!

PS: My site is has maintenance mode setup