Backround image repeat-x problem

Because of IE problems with CSS gradient property I tried to use PNG strip instead:
https://edumoto.net/

background:url(‘images/pasek.png’) 0% 0% repeat-x scroll;
background-size: 2560px 2113px;
margin:0;
padding:0;

I’d like this image to fill the whole backround – from the top to the bottom of the page regardless of page content and browser type.
In Firefox it remains longer than in IE.

Does anyone knows how to manage it?
Thanks in advance!