.hidden {
    display: none;
}
.popup {
    position: fixed;
    background: white;
    border: 1px solid #ccc;
    border-radius: 5px;
    width: 280px;
    max-height: 70%;
    top: 30%;
    left: 0;
    right: 0;
    margin: auto;
    z-index: 1000;
}