$z-index-data: (
  "autocomplete-popover": 2147483647,
  "below": -1,
  "base": 0,
  "above": 1,
  "dropdown": 10,
  "nav": 20,
  "header": 30,
  "modal": 90,
  "flash": 100,
  "alert": 100,
  "sidepanel": 80,
  "sidepanel-below": 79,
  "sidepanel-above": 81
);

@function zx($level: base) {
  @if not map-has-key($z-index-data, $level) {
    @error "No z-index level found for `#{$level}`.";
  }

  @return map-get($z-index-data, $level);
}