<link href="https://fonts.googleapis.com/css2?family=Damion&display=swap" rel="stylesheet">

<button class="noselect">Rainbow v2</button>

* {
	margin: 0;
	padding: 0;
	box-sizing: border-box;
}

body {
	height: 100vh;
	overflow: hidden;
	display: flex;
	align-items: center;
	justify-content: center;
	background: #6dd6d1;
}

.noselect {
  -webkit-touch-callout: none;
    -webkit-user-select: none;
     -khtml-user-select: none;
       -moz-user-select: none;
        -ms-user-select: none;
            user-select: none;
		-webkit-tap-highlight-color: transparent;
}

button {
	width: 150px;
	height: 50px;
	cursor: pointer;
	background: #6dd6d1;
	border: none;
	border-radius: 10px;
	box-shadow: 0px 10px 25px #57aba7, 0px -10px 25px #a6fffa, inset 0px -5px 10px #57aba7, inset 0px 5px 10px #a6fffa;
	font-family: 'Damion', cursive;
	color: white;
	font-size: 20px;
	transition: 500ms;
}

button:hover {
		border: 2px solid #6dd6d1;
	animation: hueRotation 2s linear infinite;
}

@keyframes hueRotation {
	to {filter: hue-rotate(360deg);}
}

button:focus {
	outline: none;
}