#quick-checkout-modal {
    position: fixed;
    top: 0; left: 0;
    width: 100%; height: 100%;
    background: rgba(0,0,0,0.6);
    z-index: 9999;
    display: flex;
    justify-content: center;
    align-items: center;
}
#quick-checkout-modal .modal-content {
    background: #fff;
    padding: 20px;
    width: 90%;
    max-width: 500px;
    border-radius: 5px;
    position: relative;
}
.modal-close {
    position: absolute;
    right: 10px;
    top: 10px;
    cursor: pointer;
    font-size: 20px;
}