Add image lightbox overlay and icon


Today, when activating lightbox for an image block or using lightbox action link, we have no option to easily add an overlay or icon over the image to show that it is clickable.

We can use CSS pseudo element with a class to add an overlay, but then we can only use CSS content property for the text/icon, which is very limitating.

It would be nice to have an option to choose overlay / text / icon for all lightbox elements.

The only solution I could find for this is manually adding an absolute div with an icon, which is a pain since you need to duplicate the whole structure for each block, and each further edit has to be repeated for all blocks again.
This is OK inside a query since you set this in the query template, but not OK in the general case.

To go a bit further, what would be even better is the ability to use a global class (or setting?) to set overlay and icon, so that we can easily have a consistent and maintainable behaviour sitewise.