How to make background change over time?

Hi Susan.  I hope you're well on your way to recovering from being sick. And not to worry—the community has you covered for figuring out this visual effect.

Phil's suggestion is spot on. The simplest way to make this work is to put a semi-transparent rectangle over top of your photo and have it animate onto the slide. To make it even easier to figure out, I've attached a Storyline file where I followed his instructions for recreating that slide effect. I hope that helps and let us know if you have any follow up questions!