Jetpack_Custom_CSS_Enhancements::style_filter PHP Method

    static function style_filter($current)
    {
        if (is_admin()) {
            return $current;
        } elseif (self::is_freetrial() && (!self::is_preview() || !current_user_can('switch_themes'))) {
            return $current;
        } elseif (self::skip_stylesheet()) {
            /** This filter is documented in modules/custom-css/custom-css.php */
            return apply_filters('safecss_style_filter_url', plugins_url('custom-css/css/blank.css', __FILE__));
        }
        return $current;
    }