docs: def closestsites(struct_blk, struct_def, pos):
      """
      Returns closest site to the input position
      for both bulk and defect structures
      Args:
          struct_blk: Bulk structure
          struct_def: Defect structure
          pos: Position
      Return: (site object, dist, index)
      """
      blk_close_sites = struct_blk.get_sites_in_sphere(pos, 5, include_index=True)
      blk_close_sites.sort(key=lambda x: x[1])
      def_close_sites = struct_def.get_sites_in_sphere(pos, 5, include_index=True)
      def_close_sites.sort(key=lambda x: x[1])
  
      return blk_close_sites[0], def_close_sites[0]