I’m having an interesting experience with Interactions that target an HTML Embed.
The Embed houses a MailChimp newsletter form (and for the first time, an embed is actually rendering in Designer. That’s a first!).
What I’m trying to do, essentially:
When I created a button above it that would allow people to click to expand the subscribe form, I get all the way to the point where select the embed, to add it as a targeted element in the Interactions panel successfully. But once I click on “Display:none” to create the initial state the entire 
Designer goes all grey/white. Stuck.
My project needs to remain private as it’s for a client, but let me know if you’re able to reproduce this out there.
For now, I’m skipping transitions on it.