body {
    margin: 0;
    overflow: hidden;
}

#center {
    width: 100vw;
    height: 100vh;

    display: flex;
    justify-content: center;
    align-items: center;
}

#img {
    max-width: 100%;
    max-height: 100%;

    object-fit: contain;

    opacity: 0;
    transition: opacity 2s ease;
}