How to set page div width 100% with background color

Hello,

I want to set a div with 100% width behind the header/menu or set this section at 100% width, but with centered content (logo, search and menu).

When I add a div before ‘page’ the div appears, but then my content section below isn’t centered anymore but aligns to the left site.

Using Chrome and the “inspect elements” option it seams the class hfeed in the div ‘page’ is the thing to change, but that class has nothing to do with layout i’ve read.

How can I make this work?