How do i add empty space to my Navigation bar?

[max001]

http://i.stack.imgur.com/mDS5o.pngI basically would like to add empty space either side of that nav bar so it follows all the way to the end of the screen. If it was possible being able to do so it would fit any screen size would be great! I've been coding for two days now learning from codeacademy so i dont have the full knowledge of how to do little things like this.Your help is much appreciated.(the empty space either side of the nav bar should match the nav bars props, i.e opacity, size)Also I would much rather if someone could explain to me how its done as I have noticed alot of the questions asked here are answered with the exact code required and a copy + paste is all that's needed.