Solved: Website background on Chrome Mobile is bumpy

On Chrome Mobile, the background of my website is very bumpy and glitches up and down with white sections. As far as I know it's because of the URL bar that hides.

• Example: http://ift.tt/1EfAbAL

The CSS I use to add the background:

html {
  background: url(user-images/background.png) no-repeat center center fixed;
  background-size: cover;
}

• Demo: http://ift.tt/1B1u6qF


• Source: http://ift.tt/17m7WDp

I'd like to fix this using CSS, but if I have to use Javascript I'd really like a simple explanation of how it works and how I should add it to my code, since I haven't used any Javascript yet.

Thanks in advance!