body {
    margin: 0;
    overflow: hidden;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background: white;
}

img {
    max-width: 100vw;
    height: auto;
    transition: transform 4s ease-out;
    transform: scale(2.5); /* zoom initial */
    display: block;
}

img.zoom-out {
    transform: scale(1); /* dézoom final */
}