Page region CSS class not applied
Nevermind I read on attributes: https://www.drupal.org/docs/8/theming-drupal-8/using-attributes-in-templates 

The attribute I was referencing 'highlighted_attributes' was blank. I just added a simpler solution, by referecing to the example of the API:

{% set classes = [ 'red', 'green', 'blue' ] %}

&lt;div{{ attributes.addClass(classes) }}&gt;&lt;/div&gt;