.container {
  height: 300px;
  position: relative;
}
.item {
  width: 50px;
  height: 50px;
  border-radius: 5px;
  background-color: #123;
  position: absolute;
  top: 50px;left: 0;right: 0;
  margin: auto;
  animation: animeSample 1s ease .5s forwards;
}
@keyframes animeSample {
  0% { top: 50px; }
  100% { top: 5px; }
}