How do I customize bootstrap‘s $form-validation-state?

css   
@import "~bootstrap/scss/functions";
@import "~bootstrap/scss/variables";
@import "~bootstrap/scss/mixins";

$custom-validation-states: (
  "invalid": (
    "background-color": black,
  ),
);

$form-validation-states: map-merge(
  $form-validation-states,
  $custom-validation-states
); 

@import "~bootstrap/scss/bootstrap";