#popup {
    display: none;
    position: fixed;
    z-index: 1000;
    left: 0;
    top: 0;
}

#popup img {
    box-shadow: 0 0 5em 0 rgba(0, 0, 0, 0.5);
    text-align: center;
    position: relative;
    max-width: 100%;
    max-height: 100%;
}