body {
  /* Location of the image 
  background-image: url(images/background31.jpg);  */
  background: url(../images/rotar_img.php) ;  
  background-position: center center;  
  background-repeat: no-repeat;  
  background-attachment: fixed;
  background-size: cover;   
  background-color:rgb(220, 220, 220);
  
    
  
  /* SHORTHAND CSS NOTATION
   * background: url(background-photo.jpg) center center cover no-repeat fixed;
   */
}

/*en el html debajo del body agregar un div vacio con el id rotator
 <div id="rotator">&nbsp;</div> 
 esto hace que el background sea random, y toma todas las imagenes que exista en la carpeta donde se encuentra el rotar_img.php
 */ 
#rotator {
   background: url(../images/rotar_img.php) ;  
  color: inherit;
  height: 100%;
  width: 100%;	
  background-position: center center;  
  background-repeat: no-repeat;  
  background-attachment: fixed;
  background-size: cover;  
  background-color:#464646;
    
  
}



/* For mobile devices */
@media only screen and (max-width: 760px) {
  body {
    /* The file size of this background image is 93% smaller
     * to improve page load speed on mobile internet connections */
    background-image: url(../images/bgChica.jpg);
  }
}