private void btnThannhan_Click(object sender, EventArgs e)
        {
            frmThanNhan frmtn = new frmThanNhan();

            frmtn.Show();
            this.Hide();
        }
        private void quảnLýThânNhânToolStripMenuItem_Click(object sender, EventArgs e)
        {
            frmThanNhan frmtn = new frmThanNhan();

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