.loader {
  width: 2vw;
  aspect-ratio: 1;
  --c: no-repeat linear-gradient(#000 0 0);
  background: 
    var(--c) 0%   50%,
    var(--c) 50%  50%,
    var(--c) 100% 50%;
  background-size: 20% 100%;
  animation: l1 1s infinite linear;
  margin-top: 40vh;
  margin-left: 49vw;
  transition-duration: 0.2s;
}
@keyframes l1 {
  0%  {background-size: 20% 100%,20% 100%,20% 100%}
  33% {background-size: 20% 10% ,20% 100%,20% 100%}
  50% {background-size: 20% 100%,20% 10% ,20% 100%}
  66% {background-size: 20% 100%,20% 100%,20% 10% }
  100%{background-size: 20% 100%,20% 100%,20% 100%}
}