Testing and validating CSS elements on native mobile apps

I need to inspect the CSS elements for a mobile app that I'm testing. I need to validate the fonts, colors etc. On a web app this is very simple, but I don't know how to view the CSS on a native mobile app. The app is developed for both iOS and one for android. For iOS we use TestFlight to install the latest build. For Android we use gethub to download the latest apk. We are also transitioning to Flutter, so some screens are native and some are developed in Flutter. . Any help or advice would be appreciated. Thank you.