@keyframes square-spin {
  25% {
    transform: perspective(100px) rotateX(180deg) rotateY(0); }
  50% {
    transform: perspective(100px) rotateX(180deg) rotateY(180deg); }
  75% {
    transform: perspective(100px) rotateX(0) rotateY(180deg); }
  100% {
    transform: perspective(100px) rotateX(0) rotateY(0); } }

.square-spin > div {
  animation-fill-mode: both;
  width: 50px;
  height: 50px;
  background: #6b6f82;
  animation: square-spin 3s 0s cubic-bezier(0.09, 0.57, 0.49, 0.9) infinite; }