How to set a border:

To set a border, first, get into widget mode. Then, click the pencil icon of the widget. Next, click style and then click border. Finally, set the edges width and color.

With EXAI web builder you can apply borders to any part of the page:

Here is how to set a border:

Login to your EXAI account and open the website in widget mode.
Step 2: Click on STYLE (A).
Step 3: Click on BORDER (B). 
Step 4: Configure your edges (C), width (D), and color (E). 
Step 5: Click DONE.