#redscanline {
    position: fixed;
    top: 0;        
    left: 0;
    width: 100%;
    height: 2px;       
    background: red;
    opacity: 0.3;
    z-index: 9999;

    animation: moveDown 6s linear infinite;
}

@keyframes moveDown {
    0% {
        top: 0px;
    }
    100% {
        top: 100%;
    }
}