<hr />

body {
  padding: 1rem;
}

hr {
  animation: AnimationEffect 4s ease infinite;
  border: none;
  background: linear-gradient(
    270deg,
    #349179,
    #5789da,
    #35a4b0,
    #7ca58a,
    #35a4b0,
    #5789da,
    #349179
  );
  background-size: 400% 100%;
  height: 8px;
}

@keyframes AnimationEffect {
  0% {
    background-position: 0% 50%;
  }
  50% {
    background-position: 100% 50%;
  }
  100% {
    background-position: 0% 50%;
  }
}