public function setCssFile($cssFile)
    {
        if (!$this->cssFileIsCached($cssFile)) {
            $absoluteFileName = GeneralUtility::getFileAbsFileName($cssFile);
            if (($cssFile !== '') && is_readable($absoluteFileName)
            ) {
                self::$cssFileCache[$cssFile] = file_get_contents($absoluteFileName);
            } else {
                self::$cssFileCache[$cssFile] = '';
            }
        }

        $this->setAsString('cssFile', self::$cssFileCache[$cssFile]);
    }