background image size increases based on pixel 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: how to scale a bg image acc to size of div

/* One way */
background-size: cover;

/* Other option */
background-size: contain;