private void btnQuayLai_Click(object sender, EventArgs e)
        {
            this.Close();
            FormKiemTraKhachHang FKTKH = new FormKiemTraKhachHang();

            FKTKH.Show();
        }
        private void btnLapHoaDon_Click(object sender, EventArgs e)
        {
            FormKiemTraKhachHang FKTKH = new FormKiemTraKhachHang();

            FKTKH.Show();
            this.Hide();
        }