private void btnBaoCao_Click(object sender, EventArgs e)
        {
            dgvDanhSach.DataSource = SachBUS.BaoCaoNhapKho(dtkNgay.Value);
            Custom();
            dgvDanhSach.ClearSelection();
            int TongCong = 0;

            for (int i = 0; i < dgvDanhSach.RowCount; i++)
            {
                TongCong = TongCong + int.Parse(dgvDanhSach.Rows[i].Cells[2].Value.ToString());
            }
            txtTongcong.Text = TongCong.ToString();
        }