Return `w:style[@w:type="*{style_type}*][-1]` or |None| if not found.

def default_for(self, style_type):
        """
        Return `w:style[@w:type="*{style_type}*][-1]` or |None| if not found.
        """
        default_styles_for_type = [
            s for s in self._iter_styles()
            if s.type == style_type and s.default
        ]
        if not default_styles_for_type:
            return None
        # spec calls for last default in document order
        return default_styles_for_type[-1]