animate.css/source/flash.css

@-webkit-keyframes flash {
	0%, 50%, 100% {opacity: 1;}	
	25%, 75% {opacity: 0;}
}

@-moz-keyframes flash {
	0%, 50%, 100% {opacity: 1;}	
	25%, 75% {opacity: 0;}
}

@-o-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;
	-moz-animation-name: flash;
	-o-animation-name: flash;
	animation-name: flash;
}