Problems with mobile Background

Hey!

I´m new here, not an expert in WordPress an CSS.
I´m building a site for a friend with a small business.

The free Zerif Lite Theme is awesome, thanks at first!
Now i have a Problem with the background at mobile diveces.
Something i changed in the CSS-Code crashed the parallax effect and creates space above the nav- and header-area. I tried to find the Problem for hours….

Thanks in advance!

Two Screenshots:
http://test.sokola.de/wordpress/wp-content/uploads/2016/04/Datei_001.png
http://test.sokola.de/wordpress/wp-content/uploads/2016/04/Datei_002.png

The Code
http://pastebin.com/3ghPeUT0