$(document).ready(function(){

    $('.down-list').width($('.dropdown-menu').width()-2);

    $('.dropdown-menu').hover(
      function () {
        $('.menu-first', this).addClass('slide-down'); 
        $('.down-list', this).slideDown(400);
      }, 
      function () {
        obj = this;
        $('.down-list', this).slideUp(300, function(){ $('.menu-first', obj).removeClass('slide-down'); });
      }
    );

});