<div id="preloader"></div>

#preloader {
  height: 50px;
  width: 50px;
  margin: 40vh auto;
  border: 5px solid rgba(60,60,180,0.45);
  border-top: 5px solid rgb(60,60,180);
  border-radius: 50%;
  animation: rotate 1s infinite linear;
}

@keyframes rotate {
  0% {
    transform: rotate(0deg);
  }
  100% {
    transform: rotate(360deg);
  }
}