private void nhàCungCấpToolStripMenuItem_Click(object sender, EventArgs e)
 {
     NhaCungCap frm = new NhaCungCap();
     frm.MdiParent = this;
     frm.Show();
 }
 private void buttonItem5_Click(object sender, EventArgs e)
 {
     NhaCungCap ncc = new NhaCungCap();
     ncc.MdiParent = this;
     ncc.Show();
        // this.Hide();
 }