Inlined contents are wrapped in a div that contains this class (among other things). Its purpose is to encapsulating the content into a box.
overflow: hidden; position: relative for this purpose. Of course, this
is not perfect encapsulation, you can escape it - but you shouldn’t.
This is part of the Boomla philosophy borrowed from the concepts of functional
programming. In the future, the platform will take further actions to enforce
that contents are forced into their containing boxes.
Note that any time you want to a show an overlay greater than your box, you could as well increase your content size instead, to have enough space. For example, instead of a dropdown menu that shows an overlay, just show it inline.