We broke app-auth dialogs (e.g. portal's permission prompt with 5f7d38bd but only since app-auth was just lucky to get it right before. Fix this, a leak in app-auth-prompt and clean up a bit around the edges.
I've moved the system-modal dialog related style changes here too:
- always add a top and bottom margin so the top bar / home bar isn't occluded by dialog content
- fix padding around title