private void btnHDXuat_Click(object sender, EventArgs e)
        {
            this.Hide();
            frmHoaDonXuat HDX = new frmHoaDonXuat();

            HDX.ShowDialog();
            this.Show();
        }
        private void bánHàngToolStripMenuItem_Click(object sender, EventArgs e)
        {
            this.Hide();
            frmHoaDonXuat Xuat = new frmHoaDonXuat();

            Xuat.ShowDialog();
            this.Show();
        }