adapt background size code example
Example 1: css background image size fit screen
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;
}
Example 2: background image height and width
.class{
background: url("../images/icons/map.png") no-repeat center center/50px 50px fixed;
}