canvas {
    position: absolute; 
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    opacity: 0.5;
    animation: hidden infinite 15s ease-in-out;
}
@keyframes hidden {
    0% {
        opacity: 0.5;
    }


    40% {
        opacity: 0.4;
    }

    50% {
        opacity: 0.5;
    }

    75% {
        opacity: 0.4;
    }

    100% {
        opacity: 0.5;
    }
}