#custom-lightbox {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;

    display: none;
    background: rgba(0,0,0,0.8);

    z-index: 999999; /* VERY IMPORTANT */

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

#custom-lightbox img {
    max-width: 90%;
    max-height: 85%;
    border-radius: 8px;
}

#lightbox-close {
    position: absolute;
    top: 20px;
    right: 30px;
    font-size: 35px;
    color: #ffffff;
    font-weight: bold;
    cursor: pointer;
    z-index: 1000000; /* higher than popup */

    background: rgba(0,0,0,0.5);
    padding: 5px 12px;
    border-radius: 50%;
}