$z-index: (
  modal: var(--modal-index),
  navigation: var(--navigation-index),
  scroll-to-top: var(--scroll-to-top-index),
  above-search: var(--above-search-form-index),
  search: var(--search-form-index),
  above-content: 1,
  content: 0,
  below-content: -1,
);

@mixin customZindex($key) {
  z-index: map.get($z-index, $key);;
}