/* animation for newly displayed buttons */
@keyframes popIn {
  from {
    transform: scale(0.7);
    opacity: 0;
  }
  to {
    transform: scale(1);
    opacity: 1;
  }
}

button.pop-in {
  animation: popIn 0.3s ease forwards;
}


@keyframes fadeOut {
  0% {
    opacity: 1;
    transform: scale(1);
  }
  100% {
    opacity: 0;
    transform: scale(0);
  }
}
.flip-card.matched {
  animation: fadeOut 0.6s ease forwards;
  pointer-events: none;
}