docs: def resolve_theme(self, name):
          """
          From given theme name, return theme file path from
          ``settings.CODEMIRROR_THEMES`` map.
  
          Arguments:
              name (string): Theme name.
  
          Raises:
              KeyError: When given name does not exist in
                  ``settings.CODEMIRROR_THEMES``.
  
          Returns:
              string: Theme file path.
          """
          if name not in settings.CODEMIRROR_THEMES:
              msg = ("Given theme name '{}' does not exists in "
                     "'settings.CODEMIRROR_THEMES'.")
              raise UnknowThemeError(msg.format(name))
  
          return settings.CODEMIRROR_THEMES.get(name)