You can now set an overlay effect for the columns for when the column is hovered by mouse. Click on the edit column icon and go to Overlay Options. Add your check mark the option to enable it, set the link and the background color for the column when the mouse is hovered over it (you can change the opacity to make the overlay transparent.
Up to this part you have only set the link and color for the overlay, to add content to the overlay just add content to the column just like you regularly do, and it will appear as overlay content.
For example add a text module and then add an icon and a title to it. That’s it, save it and you are good to go.