code: function unsubscribe(f) {
      return function () {
  
        // remove from fitties array
        fitties = fitties.filter(function (_) {
          return _.element !== f.element;
        });
  
        // stop observing DOM
        if (f.observeMutations) {
          f.observer.disconnect();
        }
  
        // reset font size to inherited size
        f.element.style.cssText = f.originalStyle;
      };
    }
docs: remove an existing fitty