Add Border/Shadow Options to In-App Hub 2.0 Themes

We need to be able to add a border or shadow to the 2.0 hub As you can see in this screenshot, when we use our corporate style guide it blends into the app too much. I know other background colors are available, but I can only use white or this light gray. Being able to add a border or shadow would help to differentiate the hub from the background app.

An alternative would be the ability to edit CSS or HTML options (like in an engagement).