private void btnPhieuXuat_Click(object sender, EventArgs e)
        {
            frmPhieuXuat frm = new frmPhieuXuat();

            frm.Show();
        }
        private void phiếuXuấtToolStripMenuItem_Click_1(object sender, EventArgs e)
        {
            frmPhieuXuat frm = new frmPhieuXuat();

            frm.ShowDialog();
        }