html,body{
    height:100%; 
}
body {
  background: url('index.jpg') no-repeat center center fixed;
  -webkit-background-size: cover;
  -moz-background-size: cover;
  -o-background-size: cover;
  background-size: cover;
}
.wrap {
  position: relative;
  z-index: 1;
  padding-top: 20vh;
  text-align: center;
  color: #fff;
}