protected function fixUrls($cssBlocks, $originalFile) {
        foreach ($cssBlocks as $cssBlock) {
            if ($cssBlock instanceof Import) {
                $this->fixUrls($cssBlock->atRuleArgs(), $originalFile);
            } else {
                if (! $cssBlock instanceof URL) {
                    continue;
                }

                $originalUrl = $cssBlock->getURL()->getString();
                $url = $this->relativeToAbsolute($originalUrl, $originalFile);
                $cssBlock->getURL()->setString($url);
            }
        }
    }