def _process(self):
        form = CSSSelectionForm(event=self.event)
        if form.validate_on_submit():
            layout_settings.set(self.event, 'use_custom_css', form.theme.data == '_custom')
            if form.theme.data != '_custom':
                layout_settings.set(self._conf, 'theme', form.theme.data)
            flash(_('Settings saved'), 'success')
            return redirect(url_for('event_layout.index', self.event))