How to remove PageControl's border?

interface

type
  TMainForm = class(TForm)
    PageControl1: TPageControl;
    TabSheet1: TTabSheet;
  ...
    procedure FormCreate(Sender: TObject);
  ...
  private
    FOriginalPageControlWndProc: TWndMethod;
    procedure PageControlWndProc(var Message: TMessage);
  ...
  end;

 ...

implementation

 ...

procedure TMainForm.PageControlWndProc(var Message: TMessage);
begin
  FOriginalPageControlWndProc(Message);
  with Message do
  if (Msg = TCM_ADJUSTRECT) and (Message.WParam = 0) then
  begin
    InflateRect(PRect(LParam)^, 4, 4);
    Dec(PRect(LParam)^.Top, 2)
  end;
end;

procedure TMainForm.FormCreate(Sender: TObject);
var
  I: Integer;
begin
  with PageControl1 do
  begin
    for I := 0 to PageCount - 1 do
      Pages[I].TabVisible := False;
    FOriginalPageControlWndProc := WindowProc;
    WindowProc := PageControlWndProc;
    ActivePage := TabSheet1;
    Realign;
  end;
end;