A screen that adapts has to ask first: is a screen reader running, is the phone in dark mode, in the background, on a large screen, offline? React Native 36,878 answers with small APIs, most of them a getter plus an event, and expo-device and NetInfo 2,178 fill the gaps. Each demo is a screen in src/info/ of the BookNest project, run on the Android 16 emulator, with logs from Metro's terminal unless noted.