I adjusted the font from template parameter> fonts and I applied the selector ". GkMenu> ul> li", (as you already mentioned in this post: http://www.gavick.com/forums/bikestore-joomla25/change-font-size-and-family-in-the-top-menu-19306.html?p=145054).
My problem is that it updates only the first level of the menu, while the sublevels remain with the default font.