01SetTheme.dart

// Set Default Theme
// first declare a theme 
final ThemeData _kShrineTheme = _buildShrineTheme();
ThemeData _buildShrineTheme() {
  final ThemeData base = ThemeData.light();
  return base.copyWith(
    colorScheme: base.colorScheme.copyWith(
      primary: kShrinePink100,
      onPrimary: kShrineBrown900,
      secondary: kShrineBrown900,
      error: kShrineErrorRed,
    ),
    textTheme: _buildShrineTextTheme(base.textTheme),
    textSelectionTheme: const TextSelectionThemeData(
      selectionColor: kShrinePink100,
    ),
  );
  inputDecorationTheme:
  const InputDecorationTheme(
    border: OutlineInputBorder(),
  );
}
// And textTheme
TextTheme _buildShrineTextTheme(TextTheme base) {
  return base
      .copyWith(
        headlineSmall:
            base.headlineSmall!.copyWith(fontWeight: FontWeight.w500),
        titleLarge: base.titleLarge!.copyWith(
          fontSize: 18,
        ),
        bodySmall: base.bodySmall!.copyWith(
          fontWeight: FontWeight.w400,
          fontSize: 14,
        ),
        bodyLarge: base.bodyLarge!.copyWith(
          fontWeight: FontWeight.w500,
          fontSize: 16,
        ),
      )
      .apply(
        fontFamily: 'Rubik',
        displayColor: kShrineBrown900,
        bodyColor: kShrineBrown900,
      );
}