html,body{
    display: flex;
    justify-content: center;
    align-items: center;
    background-color:#161616 ;
    overflow: hidden;
    transform: scale(1.5);
}
.btn{
    padding: 15px 40px;
    border: none;
    outline: none;
    color: #FFF;
    cursor: pointer;
    position: relative;
    z-index: 0;
    border-radius: 12px;
}
.btn::after{
    content: "";
    z-index: -1;
    position: absolute;
    width: 100%;
    height: 100%;
    background-color: #333;
    left: 0;
    top: 0;
    border-radius: 10px;
}
.btn::before{
    content: "";
    background:linear-gradient(
        45deg,
        #FF0000,#FF7300,#FFFB00,#48FF00,
        #00FFD5,#002BFF,#FF00C8,#FF0000,
    );
    position: absolute;
    top: -2px;
    left: -2px;
    background-size: 600%;
    z-index: -1;
    width: calc(100% + 4px);
    height: calc(100% + 4px);
    filter: blur(8px);
    animation: glowing 20s linear infinite;
    transition: opacity .3s ease-in-out;
    border-radius: 10px;
    opacity: 0;
}
@keyframes glowing{
    0% {background-position: 0 0;}
    50% {background-position: 400% 0;}
    100% {background-position: 0 0;}
}
.btn:hover::before{
    opacity: 1;
}
.btn:active:after{
    background: transparent;
}
.btn:active{
    color:#000 ;
    font-weight: bold;
}