*{
    margin: 0;
    padding: 0;
    font-family: "Poppins", sans-serif;
}
html, 
body{
    display: grid;
    height: 100%;
    place-items: center;
    background: #000;
}

.btn a{
    position: relative;
    display: block;
    height: 70px;
    width:220px;
    background: linear-gradient(115deg, #4fcf70, #fad648, #a767e5, #12bcfe, #44ce7b  );
    text-align: center;
    border-radius: 10px;
}

.btn a span {
    height: 88%;
    width: 96%;
    background: #111;
    display: block;
    position: absolute;
    left:50%;
    top:50%;
    transform: translate(-50%, -50%);
    border-radius: 6px;
    line-height: 62px;
    color:#f5f5f5;
    font-size: 25px;
}
.btn a:hover {
    animation: animate .4s linear infinite;
}

@keyframes animate {
    100%{
        filter : hue-rotate(-360deg)
    }
}