Are you definitely talking about an app (i.e. downloaded from an app store) or are you talking about the mobile browser view? They are different things.
The view you see in DiscourseHub just reflects the web view. So any changes you make to the mobile web client will be visible within DiscourseHub.
DiscourseHub makes the view cleaner as it obviates the need to have the additional browser interface elements.
As such, if you are only concerned with the DiscourseHub view you just need to prepare your modifications and deploy them in Theme Components and/or Plugins as per normal.
Actually, just working on this and it doesn’t seem to be happening on my client’s community.
The mobile isn’t mirroring the desktop version - it’s close. But not exact. The list of topics appears alongside the relevant categories. We’re trying to show just the latest discussions only on mobile. Is there an easy way to do this in the CSS?