RGB.css

.block {
    position: relative;
    /* margin: 300px auto 0;
    width: 500px;
    height: 250px; */
    border-radius: 20px;
}

.block:before, .block:after {
    border-radius: 10px;
    content: '';
    position: absolute;
    left: -2px;
    top: -2px;
    background: linear-gradient(45deg, #fb0094, #0000ff, #00ff00,#ffff00, #ff0000, #fb0094,
        #0000ff, #00ff00,#ffff00, #ff0000);
    background-size: 400%;
    width: calc(100% + 4px);
    height: calc(100% + 4px);
    z-index: -1;
    animation: steam 20s linear infinite;
}

@keyframes steam {
    0% {
        background-position: 0 0;
    }
    50% {
        background-position: 400% 0;
    }
    100% {
        background-position: 0 0;
    }
}

.block:after {
    filter: blur(50px);
}