How to add a border to the Also Bought widget
You will find the option to add a border inside the section called Widget, in the Visual preferences, as shown below:
If you want to enable the border, you should tick the box Border. You can write which border colour you need, or just choose from the colour palette.
Here you can see the widget without the border:
After you enabled the border, the widget will look similar to the image below, of course, you can choose the best colour for your shop: