.modal-size-60x40mm {
    width: 60mm;
    max-width: 60mm;
    min-width: 60mm;
    height: 40mm;
    max-height: 40mm;
    min-height: 40mm;
    margin: auto;
}

    .modal-size-60x40mm .modal-content {
        height: 100%;
        min-height: 100%;
    }