Refresh the highlighting with the current syntax style by class.

def _syntax_style_changed(self):
        """Refresh the highlighting with the current syntax style by class."""
        if self._highlighter is None:
            # ignore premature calls
            return
        if self.syntax_style:
            self._highlighter._style = create_style_class(self.syntax_style)
            self._highlighter._clear_caches()
        else:
            self._highlighter.set_style_sheet(self.style_sheet)