body {
        width: 35em;
        margin: 0 auto;
        transition: background-color 0.3s, color 0.3s;
        background-color: rgb(0, 0, 0);
        color: rgb(255, 255, 255);
}

.image {
    position: fixed;
    top: 50%; 
    left: 0;
    transform: translateY(-50%); 
    animation: slide 4s infinite alternate linear;
    width: 200px; 
    z-index: 1000; 
}
@keyframes slide {
    0% {
        transform: translateY(-50%) translateX(0);
    }
    100% {
        transform: translateY(-50%) translateX(calc(100vw - 200px));
    }
}