How to set border:

To set border of zone, first click on design mode. Next, click the border tab and choose a zone. Then, hover over the zone and click the pencil icon. After, click the border icon.

Here is how to set border of background:

Step 1: Click the design tab. 

Step 2: Click Border tab (A). 

Step 3: Choose a zone (B). 

Step 4: Hover over the zone and click the pencil icon (same as editing a widget)

Step 5: Click the border icon (C). 

Step 6: Set the edges, width, and color.