code: function $stateEventListener(event, current, params, prev) {
          // Removes previously added css rules
          if (prev) {
            $css.remove($css.getFromState(prev).concat(dynamicPaths));
            // Reset dynamic paths array
            dynamicPaths.length = 0;
          }
          // Adds current css rules
          if (current) {
            $css.add($css.getFromState(current));
          }
        }
docs: Listen for state change event and add/remove stylesheet(s)