body  { 
  background: url(fond.jpg) no-repeat center center fixed; 
  -webkit-background-size: cover;
  -moz-background-size: cover;
  -o-background-size: cover;
  background-size: cover;
}
h1 {
 color: white;
 font-size: 1000%;
 font-family: "Arial", Helvetica, sans-serif;
}

html, body, .container {
    height: 100%;
}
.container {
    display: -webkit-flexbox;
    display: -ms-flexbox;
    display: -webkit-flex;
    display: flex;
    -webkit-flex-align: center;
    -ms-flex-align: center;
    -webkit-align-items: center;
    align-items: center;
    justify-content: center;
}