Answers for "css property to cover images in background"

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;

 }

background image height and width

.class{
	background: url("../images/icons/map.png") no-repeat center center/50px 50px fixed;
}