.glow-on-hover {
    width: 220px;
    height: 50px;
    border: none;
    outline: none;
    color: #fff;
    background: #111;
    cursor: pointer;
    position: relative;
    z-index: 0;
    border-radius: 10px;
}

.glow-on-hover:before {
    content: '';
    background: linear-gradient(45deg, #ff0000, #ff7300, #fffb00, #48ff00, #00ffd5, #002bff, #7a00ff, #ff00c8, #ff0000);
    position: absolute;
    top: -2px;
    left:-2px;
    background-size: 400%;
    z-index: -1;
    filter: blur(5px);
    width: calc(100% + 4px);
    height: calc(100% + 4px);
    animation: glowing 20s linear infinite;
    opacity: 0;
    transition: opacity .3s ease-in-out;
    border-radius: 10px;
}

.glow-on-hover:active {
    color: #000
}

.glow-on-hover:active:after {
    background: transparent;
}

.glow-on-hover:hover:before {
    opacity: 1;
}

.glow-on-hover:after {
    z-index: -1;
    content: '';
    position: absolute;
    width: 100%;
    height: 100%;
    background: #111;
    left: 0;
    top: 0;
    border-radius: 10px;
}

@keyframes glowing {
    0% { background-position: 0 0; }
    50% { background-position: 400% 0; }
    100% { background-position: 0 0; }
}







*, *::before, *::after {
	box-sizing: border-box;
}

@keyframes rotate {
	100% {
		transform: rotate(1turn);
	}
}

.rainbow {
	position: relative;
	z-index: 0;
	width: 400px;
	height: 100px;
	border-radius: 10px;
	overflow: hidden;
	padding: 2rem;
}
	
.rainbow:before {
		content: '';
		position: absolute;
		z-index: -2;
		left: -50%;
		top: -50%;
		width: 200%;
		height: 200%;
		background-color: #399953;
		background-repeat: no-repeat;
		background-size: 45% 45%, 45% 45%;
		background-position: 0 0, 100% 0, 100% 100%, 0 100%;
		background-image: linear-gradient(#399953, #399953), linear-gradient(#fbb300, #fbb300), linear-gradient(#d53e33, #d53e33), linear-gradient(#377af5, #377af5);
		animation: rotate 4s linear infinite;
	}
	
    .rainbow:after {
		content: '';
		position: absolute;
		z-index: -1;
		left: 6px;
		top: 6px;
		width: calc(100% - 12px);
		height: calc(100% - 12px);
		background: white;
		border-radius: 5px;
        
		animation: opacityChange 3s infinite alternate;
	}


@keyframes opacityChange {
	50% {
		opacity:1;
	}
	100% {
		opacity: .5;
	}
}