To add a menu border, first drag and drop a menu widget. Then, hover over the widget and click on the pencil icon. Next, click on the advanced tab. Finally, click on Menu and then click on the border tab. In this editor you can change the position, width, color, radius position, and radius.
Step 1: Get into advanced mode (See Menu Widget - Advanced).
Step 2: Click on the border tab (A).
Step 3: Adjust position (B), width (C), color (D), radius position (E), and radius (F).
Here is an example of a green border with a width of 10 px and radius of 10 px.
From within the border tab, you can change the position, width, color, radius position, and radius.
Note: The menu-border only affects the menu container and not the border around the buttons.