Jetpack_Custom_CSS_Enhancements::customize_preview_wp_get_custom_css PHP Method

    public static function customize_preview_wp_get_custom_css($css)
    {
        global $wp_customize;
        $preprocessor = $wp_customize->get_setting('jetpack_custom_css[preprocessor]')->value();
        // If it's empty, just return.
        if (empty($preprocessor)) {
            return $css;
        }
        /** This filter is documented in modules/custom-css/custom-css.php */
        $preprocessors = apply_filters('jetpack_custom_css_preprocessors', array());
        if (isset($preprocessors[$preprocessor])) {
            return call_user_func($preprocessors[$preprocessor]['callback'], $css);
        }
        return $css;
    }