var speed = 300 /* You can define the speed of the animation, in milliseconds (1000 = 1sec) */

$(document).ready(function(){
	
	
	$('.mainnav ul li').hover(function(){ 
			$(this).find('div:first').css({visibility: "visible",display: "none"}).slideToggle(speed);
       },function(){ 
        $(this).find('div:first').css({visibility: "hidden"}).slideToggle(speed);
   });
	
});