Removes a class from the top level element of the widget.

        Doesn't remove the class if it doesn't exist.

def remove_class(self, className):
        """
        Removes a class from the top level element of the widget.

        Doesn't remove the class if it doesn't exist.
        """
        if className in self._dom_classes:
            self._dom_classes = [c for c in self._dom_classes if c != className]
        return self