discourse-custom-wizard/assets/javascripts/discourse/components/custom-wizard-step-form.js

import Component from "@ember/component";
import discourseComputed from "discourse-common/utils/decorators";

export default Component.extend({
  classNameBindings: [":wizard-step-form", "customStepClass"],

  @discourseComputed("step.id")
  customStepClass: (stepId) => `wizard-step-${stepId}`,
});