code: function(border) { 
          if (border != undefined) {
              this.border = border;
          }
          
          if (this.div != null) {
              this.div.style.border = this.border;
          }
      }
docs: Method: setBorder
  Sets the border style of the popup.
  
  Parameters:
  border - {String} The border style value. eg 2px