code: def _load_external(self, url):
          
          if url.startswith("//"):
              # then we have to rely on the base_url
              if self.base_url and "https://" in self.base_url:
                  url = "https:" + url
              else:
                  url = "http:" + url
  
          if url.startswith("http://") or url.startswith("https://"):
              css_body = self._load_external_url(url)
          else:
              stylefile = url
              if not os.path.isabs(stylefile):
                  stylefile = os.path.abspath(
                      os.path.join(self.base_path or "", stylefile)
                  )
              if os.path.exists(stylefile):
                  with codecs.open(stylefile, encoding="utf-8") as f:
                      css_body = f.read()
              elif self.base_url:
                  url = urljoin(self.base_url, url)
                  return self._load_external(url)
              else:
                  raise ExternalNotFoundError(stylefile)
  
          return css_body
docs: loads an external stylesheet from a remote url or local path