Skeleton with pure css

skeleton.css

.skeleton {
  background: linear-gradient(90deg, rgba(250,250,250,1), rgba(200, 199, 199));
  background-size: 400% 400%;
  animation: loadingAnimation 3s ease-in-out infinite;
}

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