I found the solution here:
forum.lazarus.freepascal.org/index.php/topic,17746.msg98569.html#msg98569
uses JwaUxTheme;
Procedure TForm1.FormCreate(Sender: TObject);
Begin
//EnableTheming(False); // This is System Wide!!! Bad Idea!!! Please do NOT do this!!!
SetThemeAppProperties(0); // This effects only the Application. Better, but NOT exceptable.
end;
Procedure TForm1.FormClose(Sender: TObject; Var CloseAction: TCloseAction);
Begin
//EnableTheming(True);
end;
'Use manifest file to enable themes (Windows only)' should be unchecked.