body {
    background: url("//photo.tuchong.com/1019978/f/21914120.jpg") fixed center center;
    background-repeat: no-repeat;
    background-size: cover;
}
#matrixBG{
    position: fixed; top:0; left: 0; 
    z-index: -1;
    animation: fade8 3s infinite;
}
@keyframes fade8 {
    0% {
        opacity: 0.8;
    }
    50% {
        opacity: 0.9;
    }
    100% {
        opacity: 0.8;
    }
}