nextButtonStyle property
Style for the button that advances to the next step.
Properties set here win. Anything left null falls back to the default —
a CarpColors.primary background — and then to the ambient
ElevatedButtonThemeData, so overriding only shape keeps the default
colour. Pass a backgroundColor to change the colour too.
The label is drawn white unless a foregroundColor is given here.
Implementation
final ButtonStyle? nextButtonStyle;