Pulling in feedback from the FSE Outreach program's Build A Block Theme exploration:
There is an empty style sheet added when a blank theme is created with CBT plugin. But adding CSS to it doesn’t work until a functions.php is added to enqueue it. I think that style.css should automatically be enqueued or that a functions.php with the enqueue should be included. I am trying to use only the editor, but think that if the stylesheet is there, it should be usable.