.come-in {
  animation: come-in 0.4s ease forwards;
}
come-in:nth-child(odd) {
  animation-duration: 0.6s;
}

@keyframes come-in {
  from { transform: translateY(150px); }
  to { transform: translateY(0); }
}

<script type="text/javascript" src="flex_viewport.js" ></script>