Limit Logo/Menu width to page content width, without shrinking header

Latest Customizr
I have an odd question; I’ve found lots of ways to restrict header width on wide displays (1920 etc.), but I don’t want to do that, because I like the solid line underneath going straight across on header/footer.

Instead, I’d like to have the logo hug the left margin of the content width, and the menu hug the right margin of the content width (content width is about 70% of total width), without breaking responsive/lower resolutions.

To illustrate with ascii art, the header looks like this now:

L          Menu
---------------
   xxxxxxx

Whereas I want it to look like:

L   Menu
---------------
   xxxxxxxxx

(hopefully backticks support space formatting, if not I’ll reply with blockquote)

So I can mess with that by using padding/margin on the brand/navbar class, but won’t that break responsive by inserting a bunch of unnecessary space?