border under main menu items, moved up

Hi, I like that bottom bordrer to be up higher, under main menu links, especially with larger logos… so I always move it up with this css:

.avia-menu-fx { bottom: 25px; }

But I notice with some sites, depending on the size of logo area, when you scroll down the page, that undreline/border ends up striking through or covering on top of menu item… would there be more code I could place so it stays there or goes on top of menu item when scrolling down?