function SetWindowTheme(hWnd: Cardinal; Optional, pszSubAppName: PChar): Cardinal; stdcall; external 'uxtheme';
procedure TForm1.FormCreate(Sender: TObject);
begin
SetWindowTheme(Panel1.Handle, nil, ''); SetWindowTheme(Button1.Handle, nil, '');
SetWindowTheme(GroupBox1.Handle, nil, ''); SetWindowTheme(BitBtn1.Handle, nil, ''); end;