statusBrightness property
What the app declared through SystemUiOverlayStyle when this shot was
captured, naming the icons — Brightness.dark is dark icons, over a
light app.
Recorded per step rather than per set, because an app that turns one screen dark turns its status bar light with it, and a set drawn at one brightness throughout would be wrong on exactly that screen. Defaulted rather than required: an app that declares no style leaves nothing to record, and dark icons are what a light app wants.
Implementation
final Brightness statusBrightness;