public static function get_browser_version_classes() {
        $classes = array();
        if (self::is_edge()) {
            $classes[] = 'edge';
        } else if (self::is_ie()) {
            $classes[] = 'ie';
            for ($i = 12; $i >= 6; $i--) {
                if (self::check_ie_version($i)) {
                    $classes[] = 'ie'.$i;
                    break;
                }
            }
        } else if (self::is_firefox() || self::is_gecko() || self::check_camino_version()) {
            $classes[] = 'gecko';
            if (preg_match('/rv\:([1-2])\.([0-9])/', self::get_user_agent_string(), $matches)) {
                $classes[] = "gecko{$matches[1]}{$matches[2]}";
            }
        } else if (self::is_chrome()) {
            $classes[] = 'chrome';
            if (self::is_webkit_android()) {
                $classes[] = 'android';
            }
        } else if (self::is_webkit()) {
            if (self::is_safari()) {
                $classes[] = 'safari';
            }
            if (self::is_safari_ios()) {
                $classes[] = 'ios';
            } else if (self::is_webkit_android()) {
                $classes[] = 'android'; // Old pre-Chrome android browsers.
            }
        } else if (self::is_opera()) {
            $classes[] = 'opera';
        }
        return $classes;
    }