how to give height and width to background url in css code example

Example 1: how to set background image 100 height

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 change the width of a background image in css

#example1 {		/* Example1 has an auto background size */
  background: url(mountain.jpg);
  background-repeat: no-repeat;
  background-size: auto;
}

#example2 {		/* Example2 has an fixed background size */
  background: url(mountain.jpg);
  background-repeat: no-repeat;
  background-size: 300px 100px;
}