@function border-radius($key) {
  @if map-has-key($border-radiuses, $key) {
    @return map-get($border-radiuses, $key);
  }
  @warn "Unknown `#{$key}` in $border-radiuses.";
  @return null;
}

@function box-shadow($key) {
  @if map-has-key($box-shadows, $key) {
    @return map-get($box-shadows, $key);
  }
  @warn "Unknown `#{$key}` in $box-shadows.";
  @return null;
}

@function border($key) {
  @if map-has-key($borders, $key) {
    @return map-get($borders, $key);
  }
  @warn "Unknown `#{$key}` in $borders.";
  @return null;
}