Adapt/disable jQuery code for mobile view in css

I have sticky header in my website. When I tried to optimize my header for mobile, everything was ok but, when it became sticky it resize him or something like that so my navigation is not visible. I want to know is there any way to change jQuery code in css so my header doesn't resize when it became sticky.

Here is my code example: http://codepen.io/anon/pen/JKXYpa

Note: If you want to see where is the problem, just resize your browser on width < 480px.