Centering Nav Bar elements in a theme

Hello all,

Just a quick question. I want to know how we can center navigation bar elements. I tried using text-align: center, but it would not work. I used "margin-left: 33%", but it seems to be a sloppy fix, since it changes position, depending on the window's size (on Chrome).

Here's the test site, which i'm trying to fix.

I know the theme (Arras) is different and not part of WPMU DEV, but i just wanted to know if anyone knows the answer on top of their head.

Thank you guys!