/* extra css */
@keyframes flash {
  0% { background-color: white; } /* Initial background color */
  50% { background-color: yellow; } /* Flash color */
  100% { background-color: white; } /* Return to initial color */
}

.flash-once {
  animation: flash 0.5s ease-in-out forwards; /* 0.5s duration, ease-in-out timing, forwards fill-mode */
}