Header 'content' width

Hi.

I’m trying to edit the width of the header in the theme.
And what i mean by that is, when i try to change the width of my header, the whole design changes (background, border ect). I just want my menu and logo to have the same width as my content area below, which is 1170px.

With a little help from Photoshop, I have tried to illustrate how I want my header to be.
https://imageshack.com/a/img923/7083/OqikTb.jpg

Hope someone can help.
Thanks in advance.