Change the size of the background image to: width 100px, height 80px. code example

Example: 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;
}