Editing a theme

[Zylantex]

I'm currently editing the default theme on my forum to use the county colours. Sky blue and Navy Blue.

I have managed pretty ok so far and have the colours I want where I want them.
I want to set the width of the theme to 70%, no problem except for the top and bottom sections, indicated with red arrows, which obstinately remain full screen width. 

Any idea on how to set the width for these areas? Thanks.

[WallBB]

You have to add your header class and footer class in the wrapper and set the width of wrapper to be 70%.
That would make it work.
Hope it helps