html {
  height: 100%;
  min-height: 100%;
}
body {
  background: url(/birk-1.min.jpg) no-repeat center center fixed;
  -webkit-background-size: cover;
  -moz-background-size: cover;
  -o-background-size: cover;
  background-size: cover;
  height: 100%;
  margin: 0;
  min-height: 100%;
  padding: 0;
}