a

body{
	margin: 0;
	padding: 0;
	background: #000;
}
a{
	position: absolute;
	top: 50%;
	left: 50%;
	transform: translate(-50%, -50%);
	width: 200px;
	height: 60px;
	text-align: center;
	line-height: 60px;
	color: #fff;
	font-size: 24px;
	text-transform: uppercase;
	text-decoration: none;
	font-family: sans-serif;
	box-sizing: border-box;
	background: linear-gradient(90deg, #03a9f4, #f441a5, #ffeb3b, #03a9f4);
	background-size: 400%;
	border-radius: 30px;
	z-index: 1;
}
a:hover{
	animation: animate 8s linear infinite;
}

@keyframes animate{
	0%{
		background-position: 0%;
	}
	100%{
		background-position: 400%;
	}
}

a:before{
	content: '';
	position: absolute;
	top: -5px;
	left: -5px;
	right: -5px;
	bottom: -5px;
	z-index: -1;
	background: linear-gradient(90deg, #03a9f4, #f441a5, #ffeb3b, #03a9f4);
	background-size: 400%;
	border-radius: 40px;
	opacity: 0;
	transition: 0.5s;
}
a:hover:before{
	filter: blur(20px);
	opacity: 1;
	animation: animate 8s linear infinite;
}