But personally I hate sifting through conditions within anything whether it's css, js, html whatever.
I'll usually have some generic base styles on body, html then I have everything in media queries, and put the relevant styles for that breakpoint in there. I know this might not be the most efficient for file sizes etc but it works for me when it come time to make the inevitable changes when everything is finished. It can create a bit of double handling but protects against styles spelling over break points.
BTW: with scss, I replicate the whole structure in each break point, as I work up through the break points there are lots of empty spots but they are there if I need to make changes.