public void CloseTransparent()
        {
            TransparentDashboard a = (TransparentDashboard)Application.OpenForms["TransparentDashboard"];

            a.Close();
            this.Hide();
        }
        private void BtnPreview_Click(object sender, EventArgs e)
        {
            TransparentDashboard a = new TransparentDashboard();
            FrmPreview           b = new FrmPreview();

            a.Show();
            b.ShowDialog();
            a.Hide();
        }