private void toolStripMenuItem2_Click(object sender, EventArgs e)
 {
     if (_theme == null)
     {
         _theme = new FrmTheme {
             MdiParent = this
         };
         _theme.FormClosed += _theme_FormClosed;
         _theme.Show();
         _theme.StyleManager = StyleManager;
     }
     else
     {
         _theme.Activate();
         _theme.WindowState = FormWindowState.Normal;
     }
 }
 private void _theme_FormClosed(object sender, FormClosedEventArgs e)
 {
     _theme = null;
 }