html {
  background-color:green;
  background-image: url(http://www.enchantedlearning.com/europe/britain/Flagbig.GIF);
background-size:cover;
 background-attachment: fixed; 
}
 .gallery {
    background-color: #222222;
    padding: 30px;
    width: 700px;
    margin: 0 auto;
    margin-top: 30px;
    text-align:center;
 }
 
 .gallery img {
    height: 100px;
    border-width: 5px;
    border-color: #FFFFFF;
    border-style: solid;
    box-shadow: 3px 3px 5px 6px #000000;
    margin: 5px;
}