<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 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