#loader { position: fixed; align-items: center; justify-content: center; top: 50%; width: 100%; }
.loader {
  color: #f03355;
  width: 4px;
  aspect-ratio: 1;
  border-radius: 50%;
  box-shadow: 19px 0 0 7px, 38px 0 0 3px, 57px 0 0 0;
  transform: translateX(-38px);
  animation: l21 .5s infinite alternate linear;
}

@keyframes l21 {
  50%  {box-shadow: 19px 0 0 3px, 38px 0 0 7px, 57px 0 0 3px}
  100% {box-shadow: 19px 0 0 0  , 38px 0 0 3px, 57px 0 0 7px}
}