.modal-dialog.modal-sm  {
    position: absolute;
    margin: -100px -150px;
    top: 50%;
    left: 50%;
}

.modal-dialog.modal-md  {
    position: absolute;
    margin: -100px -300px;
    top: 50%;
    left: 50%;
}

.banner {
    position: fixed;
    width: 150px;
    height: 100%;
    z-index: 1000;
    background: white;
    padding: 5px;
    text-align: center;
}

.banner.right {
    right: 0px;
}