<div class="loader"></div>

.loader {
  width: 150px;
  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: load 1s infinite linear;
}
@keyframes load {
  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%}
}



body {
  margin:0;
  min-height:100vh;
  display: grid;
  place-items:center;
}