body {
  /* Location of the image */
  background-image: url(images/background-photo.jpg);
  
  /* Image is centered vertically and horizontally at all times */
  background-position: center center;
  
  /* Image doesn't repeat */
  background-repeat: no-repeat;
  
  /* Makes the image fixed in the viewport so that it doesn't move when 
     the content height is greater than the image height */
  background-attachment: fixed;
  
  /* This is what makes the background image rescale based on its container's size */
  background-size: cover;
  
  /* Pick a solid background color that will be displayed while the background image is loading */
  background-color:#ffffff;
  
  /* SHORTHAND CSS NOTATION
   * background: url(background-photo.jpg) center center cover no-repeat fixed;
   */
}
h1 {
  font-size: 400%;
  height: 400px;
}

h2 {font-size: 250%; font-weight: 400; }

/* For mobile devices */
@media only screen and (max-width: 600px) {
  body {
    /* The file size of this background image is 93% smaller
     * to improve page load speed on mobile internet connections */
    background-image: url(images/background-photo-mobile-devices.jpg);
  }
  h1 {
    font-size: 300%;
    height: 300px;
  }
  .sub-title, p {font-size: 0.8rem;}
}