code: def is_response(cls, response):
          '''Return whether the document is likely to be CSS.'''
          if 'css' in response.fields.get('content-type', '').lower():
              return True
  
          if response.body:
              # Stylesheet mistakenly served as HTML
              if 'html' in response.fields.get('content-type', '').lower():
                  return cls.is_file(response.bodyf is_response(cls, response):
          '''Return whether the document is likely to be CSS.'''
          if 'css' in response.fields.get('content-type', '').lower():
              return True
  
          if response.body:
              # Stylesheet mistakenly served as HTML
              if 'html' in response.fields.get('content-type', '').lower():
                  return cls.is_file(response.body)
docs: Return whether the document is likely to be CSS.