@function each-negative-margin($spacer-config) {
  @each $key, $spacer in $spacer-config {
    $spacer-config: map.set($spacer-config, $key, -$spacer);
  }
  @return $spacer-config;
}

$utilities: map-merge(
  $utilities,
  (
    "left": (
      property: left,
      class: left,
      variants: inset,
      values:
        map-merge(
          $spacer-config,
          (
            "0": 0px,
            "auto": auto,
          )
        ),
    ),
    "negative-left": (
      property: left,
      class: -left,
      variants: inset,
      values:
        each-negative-margin(
          map-merge(
            $spacer-config,
            (
              "0": 0px,
              "auto": auto,
            )
          )
        ),
    ),
  )
);