@-webkit-keyframes flash {
  0%, 50%, 100% {
    opacity: 1;
  }

  25%, 75% {
    opacity: 0;
  }
}

@keyframes flash {
  0%, 50%, 100% {
    opacity: 1;
  }

  25%, 75% {
    opacity: 0;
  }
}

.flash {
  -webkit-animation-name: flash;
  animation-name: flash;
}