preload.css

#loader {
  height: 100vh;
  height: calc(var(--vh, 1vh) * 100);
  width: 100vw;
  background: #222;
  position: fixed;
  z-index: 99;
}

#spinner {
  position: absolute;
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
  width: 120px;
  height: 120px;
}

#spinner .square {
  display: block;
  float: left;
  width: 40px;
  height: 40px;
  background: hsla(0, 0%, 100%, 0);
  animation: loading 1s infinite;
}

#s1.square {
  animation-delay: 0.125s;
}
#s2.square {
  animation-delay: 0.25s;
}
#s3.square {
  animation-delay: 0.875s;
}
#s4.square {
  animation: none;
}
#s5.square {
  animation-delay: 0.375s;
}
#s6.square {
  animation-delay: 0.75s;
}
#s7.square {
  animation-delay: 0.625s;
}
#s8.square {
  animation-delay: 0.5s;
}
@keyframes loading {
  0% {
    background: hsla(0, 0%, 100%, 1);
  }
  100% {
    background: hsla(0, 0%, 100%, 0);
  }
}