code: def css(self, mapping=None):
          '''Update the css dictionary if ``mapping`` is a dictionary, otherwise
          return the css value at ``mapping``.
  
          If ``mapping`` is not given, return the whole ``css`` dictionary
          if available.
          '''
          css = self._css
          if mapping is None:
              return css
          elif isinstance(mapping, Mapping):
              if css is None:
                  self._extra['css'] = css = {}
              css.update(mapping)
              return self
          else:
              return css.get(mapping) if css else Nonf css(self, mapping=None):
          '''Update the css dictionary if ``mapping`` is a dictionary, otherwise
          return the css value at ``mapping``.
  
          If ``mapping`` is not given, return the whole ``css`` dictionary
          if available.
          '''
          css = self._css
          if mapping is None:
              return css
          elif isinstance(mapping, Mapping):
              if css is None:
                  self._extra['css'] = css = {}
              css.update(mapping)
              return self
          else:
              return css.get(mapping) if css else None
docs: Update the css dictionary if ``mapping`` is a dictionary, otherwise
          return the css value at ``mapping``.
  
          If ``mapping`` is not given, return the whole ``css`` dictionary
          if available.