.light {
	width: 100px;
	height: 100px;
	border-radius: 50%;
	animation: shadow 1s infinite alternate;
}

@keyframes shadow {
	from {
		box-shadow: 0 0 55px 10px red;
	}
	to {
		box-shadow: 0 0 90px 20px red;
	}
}