Hey Erwin,
You need to add the following class to your css for the widget to work:
.hiddenByWidget { display: none; }
Have a look at this github documentation:https://github.com/remcos/ShowByCondition
I had the same issue and adding the class fixed it :)
Hope this helps!
EDIT – Do note that you need to write a microflow to determine when to show the specified container or not.
Additionally, you could also use dynamic classes – they more or less should do the same thing with maybe easier logic.