How to get rounded coloured text-boxes
 

How did they get the rounded coloured text boxes around the headings in the demo video with the seahorses?

From the look of that, I think there's a document wide background color and then a different background color for the Source column. To do this, open the Utilities panel and select 'Whole Document', change the background color from the Appearance: Color inspector, then select the Source column and do the same thing.