.btn1 {

    border: none;
    outline: none;
    color: #fff;
    background: #111;
    cursor: pointer;
    position: relative;
    z-index: 0;
    border-radius: 10px;
    padding-left: 5px;
}

.btn1:before {
    content: "";
    background: linear-gradient(
            124deg,
            #ff2400,
            #e81d1d,
            #e8b71d,
            #e3e81d,
            #1de840,
            #1ddde8,
            #2b1de8,
            #dd00f3,
            #dd00f3
    );
    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: 1;
    transition: opacity 0.3s ease-in-out;
    border-radius: 10px;
}


.btn1:after {
    z-index: -1;
    content: "";
    position: absolute;
    width: 100%;
    height: 100%;
    background: #111;
    left: 0;
    top: 0;
    border-radius: 10px;
}

.btn2 {

    border: none;
    outline: none;
    color: #fff;
    background: #111;
    cursor: pointer;
    position: relative;
    z-index: 0;
    border-radius: 10px;
}

.btn2:before {
    content: "";
    background: linear-gradient(
            124deg,
            #ff2400,
            #e81d1d,
            #e8b71d,
            #e3e81d,
            #1de840,
            #1ddde8,
            #2b1de8,
            #dd00f3,
            #dd00f3
    );
    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: 1;
    transition: opacity 0.3s ease-in-out;
    border-radius: 10px;
}


.btn2: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;
    }
}