new Utilities API - no output in compiled css

[SandyLudosky]

Based on the documentation, I have been trying to add a utility class with the new utilities API

below, a simple example to test out the new API to define custom utility classes. not working though. I have not been able to find the css output.

• I need to import bootstrap.scss because $utilities is undefined otherwise
• the goal is to add a new property to make any button rounded with a class 'button-rounded'.
• I am using the https://github.com/twbs/bootstrap-npm-starter to compile the scss files :
  the src is starter.scss and the output is starter.css

    @import "bootstrap.scss";
    @import "bootstrap/scss/utilities";
    
    $utilities: map-merge(
      $utilities,
      (
        "button-rounded": (
          property: border-radius,
          class: button-rounded,
          values: (
            null: 20px,
          ),
        ),
      )
    );

Am I getting this right ?