public function openOrchestraCss($themeId)
    {
        $tags = '';

        if (isset($this->themes[$themeId]) && isset($this->themes[$themeId]['stylesheets'])) {
            $stylesheets = $this->themes[$themeId]['stylesheets'];
            foreach ($stylesheets as $stylesheet) {
                $tags .= $this->getHtmlTag($stylesheet, self::FILETYPE_CSS);
            }
        }

        return $tags;
    }