private void btnVolver_Click(object sender, RoutedEventArgs e)
        {
            VisualizarVentas visv = new VisualizarVentas();

            visv.Show();
            this.Close();
        }
        private void btnVerVentas_Click(object sender, RoutedEventArgs e)
        {
            VisualizarVentas vv = new VisualizarVentas(nomUsuario);

            vv.Show();
            this.Close();
        }