Whats wrong here

I been changing the css a bit over the last few days on turforeningen.dk, and all of the sudden the layout whent nuts on me, completely changing into something not intended on mobile devices, among other things the body background image is "climbing up" and sits as the header background image.. it was working perfectly before i started making changes, so i guess i may have a small but significant setting or css error somewhere, i been staring myself blind on this issue - so would be great if i could get some help or a pointer on what to change or fix to bring it back.