background-size: contain !important; code example
Example 1: how to set background automatically with my screen height
body {
background-image: url("img_tree.gif");
background-repeat: no-repeat;
background-attachment: fixed;
background-position: top center;
background-size: contain;
}
Example 2: background image height and width
.class{
background: url("../images/icons/map.png") no-repeat center center/50px 50px fixed;
}