Add this code to the custom.css:

body {
background: none;
}

Hello Joomlaplates,

It still doesn't work.. my custom.css:

/* Copyright (C) YOOtheme GmbH, www.gnu.org/licenses/gpl.html GNU/GPL */

/*
* Custom Style Sheet - Use this file to style your content
*/

html {
background: url(../images/bg.jpg) no-repeat center center fixed;
-webkit-background-size: cover;
-moz-background-size: cover;
-o-background-size: cover;
background-size: cover;
}
body {
background: none;
}

I cant see any issue right now, the background image is showing right, did you fixed it.
If yes, please solve this thread.

It's solved, thanx!