@function _sort-map-keys-deep($map) {
  @if type-of($map) != map { @return $map; }
  $return-map: _new-map();
  $keys: _sort-list(map-keys($map));
  @each $k in $keys {
    $return-map: _deep-map-merge($return-map, (
      $k: _sort-map-keys-deep(map-get($map, $k))
    ));
  }
  @return $return-map;
}