docs: function DropDown(dropdown, options) {
      this.main = dropdown;
      this.$main = $(this.main);
  
      var defaultOption = {
          alignX: 'left',
          alignY: 'bottom',
          customClass: '',
          offsetX: 0,
          offsetY: 0
      };
      this.options = $.extend(defaultOption, options || {});
      this.init(this.options);
  }