Moving nav bar to the center

Hi everyone,

I’m currently working on website for my friends, so that’s not a big deal – yet, it infuriates me truly. So, the problem is: how to center navigation menu in this theme? I must admit, theme’s bit complicated – has four different stylesheets (1 default + 3 for color-schemes). And I couldn’t find any selector for navigation ul to f.e. add margin=0 auto and so on.

Looking forward to any tips ??

Ps. Let me know if you need stylesheets for inspection!