private void btn_thietbi_phong_ItemClick(object sender, ItemClickEventArgs e) { frm_thietbiphong frm = new frm_thietbiphong(); frm.TopLevel = false; pnl_main.Controls.Clear(); pnl_main.Controls.Add(frm); frm.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None; frm.Dock = DockStyle.Fill; frm.Show(); }