Remove spaces in dialog window

[Beast <beast i6x org>]

...
our @ISA = qw(Gtk2::Dialog);

sub new
{
   my ($class, $parent, $title)  = @_;
   my $self = {};
   bless($self, $class);

   $self->{win} = $class->SUPER::new($title, $parent, "modal");
...
}

In the bottom of dialog box/window, it has spaces (arround 5px) between 
the last widget and the window border. However, it's not happen with in 
the top, which no space between border and first widget.
How do I remove the additional spaces?

+---------------------+
| [widget A]
|
|
| [widget B]
|               <---- there is additional spaces here...
+---------------------+


--

--beast