Theme-switch animation length (flutter-patterns § Theming: animated
transition via ThemeExtension.lerp, ~200 ms — long enough to read as
deliberate, short enough to never gate interaction).
System status-bar / nav-bar overlay style for a given scheme.
Light theme → dark icons (visible on cream); dark theme → light icons.
Applied via the AppBar theme AND globally in the MaterialApp builder
(AppBar-less screens get no appBarTheme.systemOverlayStyle).
The wallet UI's type scale, with NO font family (FR-49 W-3, W-9): sizes,
weights and tracking from the refreshed design (Relim design-refresh spec
§3.6), colours from colors. Every slot the SDK's widgets read is
defined, so a host that supplies only some styles still gets the SDK's
sizes for the rest, never Material's defaults.