.container {
    position: relative;
    width: 100%;
    height: 600px;
}

.leaf {
    position: absolute;
    top: -100px;
    left: 50%;
    transform: translateX(-50%);
    width: 40px;
    height: 40px;
    background-image: url("leaf.png");
    background-size: cover;
    animation: fall 5s linear infinite;
}

@keyframes fall {
    0% {
        transform: translateY(-100%);
        opacity: 0;
    }
    100% {
        transform: translateY(100vh);
        opacity: 1;
    }
}