Your ATTEMPT at being responsive really isn't... or at minimum flips the bird at usability and accessibility. You're using pixel metrics so you're telling users who want elastic layout to sod off. Your toggle target is a DIV making it non-navigable, you don't mention it but your implementation would need to be scripting only telling non-script users to hit the bricks. You've got a lone anchor that should be in a H1 since it's basically the site title, and of course mated to that non-semantic markup are presentational classes, classes for nothing, and even span for nothing (since what you've got there looks to be generated content's job!)

Don't even get me started about the DIV doing NAV's job and the NAV doing HEADER's job, the broken use of percentage widths, display:table for Christmas only knows what...