weekNumberTextStyle property
Specifies the text style for the week number text in calendar.
Widget build(BuildContext context) {
   return Scaffold(
   appBar: AppBar(),
     body: Center(
       child: SfTheme(
         data: SfThemeData(
           calendarThemeData: SfCalendarThemeData(
           weekNumberBackgroundColor: Colors.blue,
           weekNumberTextStyle: TextStyle(color: Colors.grey,
           fontSize: 20),
           )
         ),
         child: SfCalendar(),
         ),
     )
  );
}
Implementation
final TextStyle? weekNumberTextStyle;