Hey @robyn_bieber! Welcome to the NotionApps community! We are launching a feature to show page content on the apps soon.
With that, you could use your own CSS for the content on the pages and it would reflect on the apps. As for the app styling, we will be adding new colours in the coming months that will allow you to make the app look closer to your business brand. Then, the only thing left would be custom font which we have not decided the timeline on yet.