html {
    
/*
    Photo by Kuba Bożanowski https://www.flickr.com/photos/jbozanowski/4850798971
    with changes
*/
  background: url(../assets/background.jpg) no-repeat center center fixed; 
  -webkit-background-size: cover;
  -moz-background-size: cover;
  -o-background-size: cover;
  background-size: cover;
}