#popup {
    width: 600px;
    background: #273047;
    box-shadow: 0 0 20px black;
    border-radius: 3px;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    z-index: 9999;
    display: none;
}

.close-popup {
    color: white !important;
    font-size: 25px;
    display: block;
    line-height: 0;
    float: right;
    padding: 16px 10px;
    cursor: pointer;
}

@media only screen and (max-width: 600px) {
    #popup {
        width: 90%;
    }

        #popup img {
            width: 100%;
        }
}