--- ---

    const
      WS_EX_LAYERED = $80000;
      LWA_COLORKEY = 1;
      LWA_ALPHA = 2;

    type
      TSetLayeredWindowAttributes = function(
        hwnd: HWND;    {handle to the layered window}
        crKey: TColor; {specifies the color key}
        bAlpha: byte;  {value for the blend function}
        dwFlags: DWORD {action}
      ): BOOL; stdcall;

    procedure TForm1.FormCreate(Sender: TObject);
    var
      Info: TOSVersionInfo;
      F: TSetLayeredWindowAttributes;
    begin
      inherited;
      Info.dwOSVersionInfoSize := SizeOf(Info);
      GetVersionEx(Info);
      if (Info.dwPlatformId = VER_PLATFORM_WIN32_NT) and
        (Info.dwMajorVersion >= 5) then
      begin
        F := GetProcAddress(
          GetModulehandle(user32), 'SetLayeredWindowAttributes'
        );
        if Assigned(F) then
        begin
          SetWindowLong(
            Handle,
            GWL_EXSTYLE,
            GetWindowLong(Handle, GWL_EXSTYLE) or WS_EX_LAYERED
          );
          F(Handle, 0, Round(255 * 80 / 100), LWA_ALPHA);
        end;
      end;
    end;