body {
  /* Location of the image */
  background-image: url(imagenes/fondoPrincipal.png);
  
  /* Background image is centered vertically and horizontally at all times */
  background-position: center center;
  
  /* Background image doesn't tile */
  background-repeat: no-repeat;
  
  /* Background image is fixed in the viewport so that it doesn't move when 
     the content's height is greater than the image's height */
  background-attachment: fixed;
  
  /* This is what makes the background image rescale based
     on the container's size */
  background-size: auto;
  
  /* Set a background color that will be displayed
     while the background image is loading */
  background-color: #ffffff;
}