docs: def get_destination(self, filepath, targetdir=None):
          """
          Return destination path from given source file path.
  
          Destination is allways a file with extension ``.css``.
  
          Args:
              filepath (str): A file path. The path is allways relative to
                  sources directory. If not relative, ``targetdir`` won't be
                  joined.
              absolute (bool): If given will be added at beginning of file
                  path.
  
          Returns:
              str: Destination filepath.
          """
          dst = self.change_extension(filepath, 'css')
          if targetdir:
              dst = os.path.join(targetdir, dst)
          return dst