This question might be of help.
If you go into the SASS files under _listview.scss, you will be able to find the class that they are talking about in that question.
should do the trick.
Use the show by condition app to check this: https://appstore.home.mendix.com/link/app/2539/First-Consulting/ShowByCondition
Create a microflow to check if the list is empty. If empty set this widget to not show this block.