code: public static List<String> getDistinctCssUrls(String htmlContent) {
  		Document doc = Jsoup.parse(htmlContent);
  		Elements els = doc.select(CSS_LINKS_SELECTOR);
  		List<String> cssFiles = new ArrayList<>(els.size());
  		for (Element e : els) {
  			String path = e.attr(HREF_ATTR);
  			if (!cssFiles.contains(path)) {
  				cssFiles.add(path);
  			}
  		}
  		return cssFiles;
  	}
docs: Finds all CSS file inclusions (looks for <code>link</code> tags for
  stylesheet files). Returns only the path or URL to the CSS file. If the
  several CSS inclusions have the same path, the path is present in the
  list only one time.
  
  @param htmlContent
  the html content that may contain external CSS files
  @return the list of found CSS inclusions (paths only) or empty if nothing
  found