A default theme that provides a very similiar UI look and feel as ArcGIS Pro. In particular, have all the widget buttons and toolbars look and act more like the Pro ribbon bar. Also provide a similar UI look for content windows.
The purpose of this theme is to provide a seamless transition between online apps and Pro for users. The use case is the development of an application that uses a web app for initial planning for an incident, but has to transition to using Pro in offline mode for onsite management of the incident.