how to center a background image code example

Example 1: css background image cover center

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: css align background image center

body{ 
   background-image: url('css.gif');
   background-repeat: no-repeat;
   background-position: center; 
 }

Example 3: move css background image

background-image: url('w3css.gif');
 background-repeat: no-repeat;
 background-attachment: fixed;
 background-position: center;