HTML / CSS - 可变大小的中心导航栏

I'm going to have a nav bar that lets a user sort through a gallery of pictures. The problem is the nav bar width is going to vary based on the size of the gallery, and when I don't set a width I can't use margin: 0 auto; to center the menu. (Instead, every shows up on the left side of the gallery container.)I'm going to have a nav bar that lets a user so