html {
  background: url("https://img4.goodfon.com/wallpaper/nbig/2/39/tokho-toukhou-devushka-fon-mech.jpg") no-repeat center center fixed;
  -webkit-background-size: cover;
  -moz-background-size: cover;
  -o-background-size: cover;
  background-size: cover;
}