def _process(self):
        f = request.files['file']
        self.event.stylesheet = to_unicode(f.read()).strip()
        self.event.stylesheet_metadata = {
            'hash': crc32(self.event.stylesheet),
            'size': len(self.event.stylesheet),
            'filename': secure_filename(f.filename, 'stylesheet.css')
        }
        db.session.flush()
        flash(_('New CSS file saved. Do not forget to enable it ("Use custom CSS") after verifying that it is correct '
                'using the preview.'), 'success')
        logger.info('CSS file for %s uploaded by %s', self.event, session.user)
        return jsonify_data(content=_css_file_data(self.event))