//using System.Windows.Forms;

DialogResult ShowMessage(string text, string caption = "")
{
    var result = DialogResult.None;
    using (Form frm = new Form())
    {
        frm.Text = caption;
        frm.MinimumSize = new Size(350, 250);
        frm.SizeGripStyle = SizeGripStyle.Hide;
        Button btn = new Button();
        frm.Controls.Add(btn);
        btn.Left = frm.ClientSize.Width - btn.Width - btn.Margin.Right;
        btn.Top = frm.ClientSize.Height - btn.Height - btn.Margin.Bottom;
        btn.Anchor = AnchorStyles.Right | AnchorStyles.Bottom;
        btn.Text = "OK";
        btn.DialogResult = DialogResult.OK;
        btn.Click += (s, e) => { ((Control)s).FindForm().Close(); };
        TextBox tb = new TextBox();
        frm.Controls.Add(tb);
        tb.Multiline = true;
        tb.ReadOnly = true;
        tb.BackColor = SystemColors.Window;
        tb.SetBounds(0, 0, frm.ClientSize.Width, btn.Top - btn.Margin.Top);
        tb.Anchor = AnchorStyles.Left | AnchorStyles.Top | AnchorStyles.Right | AnchorStyles.Bottom;
        tb.ScrollBars = ScrollBars.Both;
        tb.Text = text;
        result = frm.ShowDialog();
    }
    return result;
}