Background (base) layer dimming

I want objects on my base layer to dim (not be hidden) when a layer is shown.  Not just on the "stage" during editing, but for the end user after publication.  Based on my research here on eLearning Heroes, it seems this is not a built-in feature, and the most common solution is to create a semi-transparent object to create the effect of dimming the base layer.  I get that.

The thing is, I struggled with this issue about 4 months ago, found a solution (or so I think!), and now I can't recall how to reconstruct it.  Searching my slides, I can't locate a particular trigger, condition, or semi-transparent anything that would account for why my base layer is dimming.  I thought I'd post the story file here and see if any detectives can help me solve this mystery (and recreate this great effect!).  Many thanks in advance!

Link to slide example in Review: https://360.articulate.com/review/content/69286707-d0d8-49d7-8678-0b8c1cf49271/review

4 Replies