def _process(self):
        form = CSSSelectionForm(event=self.event, formdata=request.args, csrf_enabled=False)
        css_url = None
        if form.validate():
            css_url = get_css_url(self.event, force_theme=form.theme.data, for_preview=True)
        return WPConfModifPreviewCSS(self, self._conf, form=form, css_url=css_url).display()