body {
    font-family: sans-serif;
    text-align: center;
    margin-top: 50px;
}

.container-eg-btn-4 {
    font-family: sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    align-content: center;
    flex-wrap: wrap;
    /*margin: 0 auto 10px;*/
    /*padding: .5em;*/
    line-height: normal;
}

.container-eg-btn-4 .button {
    background: #af40ff;
    margin: 10px;
    padding: 10px;
    text-align: center;
    position: relative;
    transition: .3s;
    z-index: 1;
    color: #fff;
    cursor: pointer;
    border-radius: 12px;
    -webkit-user-select: none;
    -ms-user-select: none;
    user-select: none;
    font-weight: 700;
}

.container-eg-btn-4 .button-8:before {
    content: '';
    background: linear-gradient(225deg, #ff0000, #ff7300, #fffb00, #48ff00, #00ffd5, #002bff, #7a00ff, #ff00c8, #ff0000);
    position: absolute;
    top: 0;
    left: 0;
    background-size: 400%;
    z-index: -1;
    width: 100%;
    height: 100%;
    transition: opacity .3s ease-in-out;
    border-radius: 12px;
}

.container-eg-btn-4 .button-8:hover:before {
    animation: glowing 20s linear infinite;
}

.container-eg-btn-4 .button-8:active:before {
    background: #000137;
}

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

    50% {
        background-position: 400% 0;
    }

    100% {
        background-position: 0 0;
    }
}