how to change css menu without nav-stacked to get horizontal menu

Hello,

I use T3 Bs3 blank template and want a menu right above. I placed it in the position: head-search. Now I have a vertical menu there. But I want a horizontal menu.
I see that there is a horizontal menu when I remove nav-stacked in the ul (with Firebug in FF). But in which file (where) can I edit this to make the horizontal menu definitive?
Or is there another solution to get a horizontal menu in the top right?

Thanks
Kees