make javascript background image cover body code example

Example 1: how to cover full image in css

body {
  background-position: center;
  background-repeat: no-repeat;
  background-size: cover;
}

Example 2: 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;

 }