Please watch the linked jam video to see my comments. The builder just behaves not as expected. Not sure if it’s only in this beta version or it was there before. But in the current beta it is definitely worse.
Also I could not add a new line in the CSS tab. After refresh it started working.
I agree that there seem to be some problems with updating the canvas when using nestable elements like the nestable nav, or the nestable accordions. We will look into this!