private void btLogout_Click(object sender, EventArgs e)
        {
            DangNhap_Form frm = new DangNhap_Form();

            this.Hide();
            frm.Show();
        }
 private void btLogout_Click(object sender, EventArgs e)
 {
     DangNhap_Form frm = new DangNhap_Form();
     this.Hide();
     frm.Show();
 }