how can i change the TextStyle of showDateRangePicker() or showDateRangePicker() in flutter

Question

Want to change the TextStyle of helpText in showDateRangePicker() in Flutter.

Can anybody Help.

---

  buildMaterialDatePicker({BuildContext context, SearchVM model}) 
   async {
    final DateTimeRange picked = await showDateRangePicker(
      context: context,
      firstDate: initialDate,
      helpText: 'Select a Date or Date-Range',
      fieldStartHintText: 'Start Booking date',
      fieldEndHintText: 'End Booking date',
      currentDate: initialDate,
      lastDate: DateTime(2020, initialDate.month + 1, 
      initialDate.day),
      builder: (BuildContext context, Widget child) {
        return Theme(
          data: ThemeData.dark().copyWith(
            colorScheme: ColorScheme.dark(
              primary: Colors.greenAccent,
              onPrimary: oppColor,
              surface: Colors.greenAccent,
              onSurface: oppColor,
            ),
            dialogBackgroundColor: mainColor,
          ),
          child: child,
        );
      },
    );
  }

Solution

So, according to the answer of abbas jafary answer. I deep Dived into the Documentation of the showDateRangePicker() (you can do so using Ctrl+ Right-Clicking) and found what texstTheme it is using for that Text.

 Text(
       helpText,
       style: textTheme.overline.apply(
       color: headerForeground,),
 ),

So, Then I wrapped my Widget with Theme and updated the textTheme field.

buildMaterialDatePicker({BuildContext context, SearchVM model}) async {
    final DateTimeRange picked = await showDateRangePicker(
      context: context,
      firstDate: initialDate,
      helpText: 'Select a Date or Date-Range',
      fieldStartHintText: 'Start Booking date',
      fieldEndHintText: 'End Booking date',
      currentDate: initialDate,
      lastDate: DateTime(2020, initialDate.month + 1, initialDate.day),
      builder: (BuildContext context, Widget child) {
        return Theme(
          data: ThemeData.dark().copyWith(
            colorScheme: ColorScheme.dark(
              primary: Colors.greenAccent,
              onPrimary: oppColor,
              surface: Colors.greenAccent,
              onSurface: oppColor,
            ),

          // Here I Chaged the overline to my Custom TextStyle.
            textTheme: TextTheme(overline: TextStyle(fontSize: 16)),
            dialogBackgroundColor: mainColor,
          ),
          child: child,
        );
      },
    );
   
}