style.css

iframe{
    width:100vw;
    height:100vh;
    /*background-image: url("https://wallpapercave.com/wp/wp4831641.jpg");*/
}

body{
    margin:0;
    padding:0;
    width:100vw;
    height:100vh;
    overflow:hidden;
}

#curtain{
    width:100vw;
    height:100vh;
    position:fixed;
    top:0;
    left:0;
    background-color:black;
    opacity:1;
    /*  */
    display: flex;
    align-items: center;
    justify-content: center;
}
#loader_message{
  color:white;
  position:absolute;
  top:calc(50vh + 7em);
}
#loader,
#loader:after {
  border-radius: 50%;
  width: 5em;
  height: 5em;
}
#loader {
  margin: 60px auto;
  font-size: 10px;
  position: relative;
  text-indent: -9999em;
  border-top: 1.1em solid rgba(255, 255, 255, 0.2);
  border-right: 1.1em solid rgba(255, 255, 255, 0.2);
  border-bottom: 1.1em solid rgba(255, 255, 255, 0.2);
  border-left: 1.1em solid #ffffff;
  -webkit-transform: translateZ(0);
  -ms-transform: translateZ(0);
  transform: translateZ(0);
  -webkit-animation: load8 1.1s infinite linear;
  animation: load8 1.1s infinite linear;
  opacity:1;
}
@-webkit-keyframes load8 {
  0% {
    -webkit-transform: rotate(0deg);
    transform: rotate(0deg);
  }
  100% {
    -webkit-transform: rotate(360deg);
    transform: rotate(360deg);
  }
}
@keyframes load8 {
  0% {
    -webkit-transform: rotate(0deg);
    transform: rotate(0deg);
  }
  100% {
    -webkit-transform: rotate(360deg);
    transform: rotate(360deg);
  }
}