[cletusw]

Having two completely unrelated UIs – one for mobile, one for desktop - isn't really responsive. When done that way there's some point (e.g. 1199px width in the OP's example) where you suddenly have a tiny mobile web site with a ton of blank space on either side (or worse, it stretches it all out to fit and all the blank space is within every single button and widget).

There should either be several progressively more "mobile" breakpoints, or even better, use component queries so individual chunks of the page can rearrange their contents as their available area shrinks.