public function getStylesheet($stylesheet)
    {
        $stylesheet = $this->getStylesheetObject($stylesheet);
        $styleValues = $this->getThemeCustomStyleObjectValues();
        if (!is_null($styleValues)) {
            $stylesheet->setValueList($styleValues);
        }
        if (!$this->isThemePreviewRequest()) {
            if (!$stylesheet->outputFileExists() || !Config::get('concrete.cache.theme_css')) {
                $stylesheet->output();
            }
        }
        $path = $stylesheet->getOutputRelativePath();
        if ($this->isThemePreviewRequest()) {
            $path .= '?ts='.time();
        } else {
            $path .= '?ts='.filemtime($stylesheet->getOutputPath());
        }

        return $path;
    }