<STYLE type="text/css">

body#background 
  background: url("https://s22.postimg.org/5fxnq74g1/PSI_landing_page.jpg") no-repeat 50% 50% fixed; 
  background-size: cover;
  -moz-background-size: cover;
  -o-background-size: cover;
  -webkit-background-size: cover;
}

</STYLE>