CupertinoTheme not applyed to modals and action sheets - flutter

Question

Whats happening

• Applying a font family all over my CupertinoApp using CupertinoThemeData.
• Font family is used from google_fonts package.

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Questions/issues

• The text theme specified in CupertinoThemeData isn't applying it to CupertinoActionSheet and CupertinoAlertDialog.
• If CupertinoThemeData doesn't cover CupertinoActionSheet, CupertinoAlertDialog, etc, then how to specify a theme for them?

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Related Code Blocks

Main file, CupertinoApp:

@override
  Widget build(BuildContext context) {
    return CupertinoApp(
      title: AppConstants.name,
      home: const SomeScreen(),
      theme: CupertinoThemeData(
        textTheme: CupertinoTextThemeData(
          textStyle: AppConstants.appTextStyle,
          navLargeTitleTextStyle: AppConstants.appTextStyle.copyWith(
            fontSize: 30,
            fontWeight: FontWeight.bold,
          ),
          navActionTextStyle: AppConstants.appTextStyle.copyWith(
            color: AppConstants.primaryColor,
          ),
          navTitleTextStyle: AppConstants.appTextStyle.copyWith(
            color: CupertinoColors.label,
          ),
          actionTextStyle: AppConstants.appTextStyle.copyWith(
            color: AppConstants.primaryColor,
          ),
          tabLabelTextStyle: AppConstants.appTextStyle.copyWith(
            color: CupertinoColors.label,
          ),
          pickerTextStyle: AppConstants.appTextStyle.copyWith(
            color: CupertinoColors.label,
          ),
          dateTimePickerTextStyle: AppConstants.appTextStyle.copyWith(
            color: CupertinoColors.label,
          ),
        ),
        brightness: Brightness.dark,
        primaryColor: AppConstants.primaryColor,
        scaffoldBackgroundColor: AppConstants.bgColor,
      ),
    );

Constants used:

class AppConstants {
  static TextStyle appTextStyle = GoogleFonts.ubuntu(
    color: CupertinoColors.label,
    fontSize: 17,
  );
}

Modal popup function:

showCupertinoModalPopup(
    context: context,
    builder: (context) {
      return CupertinoActionSheet(
        title: const Text('Sort By'),
        actions: options // list of strings: ['Name', 'Date', 'Modified']
            .map(
              (option) => CupertinoActionSheetAction(
                onPressed: () {},
                child: Text(option),
              ),
            )
            .toList(),
        cancelButton: CupertinoActionSheetAction(
          onPressed: () {},
          child: const Text('Cancel'),
        ),
      );
    },
  );