public function getCSSClassString()
    {
        $classes = array('swat-message');

        // legacy style for backwards compatibility
        if ($this->type === 'notice') {
            $classes[] = 'swat-message-notification';
        }

        // type-specific style
        if ($this->type != '') {
            $classes[] = 'swat-message-' . $this->type;
        }

        if ($this->secondary_content !== null) {
            $classes[] = 'swat-message-with-secondary';
        }

        return implode(' ', $classes);
    }