@keyframes soft-glow {
  0% { box-shadow: 0 0 0 rgba(99, 102, 241, 0.0); }
  50% { box-shadow: 0 0 24px rgba(99, 102, 241, 0.25); }
  100% { box-shadow: 0 0 0 rgba(99, 102, 241, 0.0); }
}

#spin-btn:not(:disabled) {
  animation: soft-glow 2.2s ease-in-out infinite;
}