$( document ).ready(
	function()
	{
		var menuElements = $( "#topmenu-firstlevel>li" );
		if( menuElements.length > 0 )
		{
			menuElements.each(
				function(index, item)
				{
					var main_menu_width = $( item ).width();
					var sub_menu_width = $( item ).children( 'div.sub_menu' ).width();
					$( item ).children( 'div.sub_menu' ).css( 'left', -1 * ( ( sub_menu_width - main_menu_width ) / 2 + 4 )  );
				}
			);
			$( menuElements ).mouseenter(
				function(e)
				{
					$( this ).children( 'div.sub_menu' ).show();
				}
			);
			$( menuElements ).mouseleave(
				function(e)
				{
					$( this ).children( 'div.sub_menu' ).hide();
				}
			);
		}
	}
);