Add `cancelButtonStyle` & `confirmButtonStyle` to the `DatePickerThemeData` (#132847)

fixes [Unable to adjust the color for "Cancel" and "Ok" button in datePicker dialog](https://github.com/flutter/flutter/issues/127739)

### Code sample

<details> 
<summary>expand to view the code sample</summary> 

```dart
import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        useMaterial3: true,
        datePickerTheme: DatePickerThemeData(
          cancelButtonStyle: TextButton.styleFrom(
            shape: const RoundedRectangleBorder(
              borderRadius: BorderRadius.all(Radius.circular(16)),
              side: BorderSide(color: Colors.red),
            ),
            backgroundColor: Colors.white,
            foregroundColor: Colors.red,
            elevation: 3,
            shadowColor: Colors.red,
          ),
          confirmButtonStyle: TextButton.styleFrom(
            shape: const RoundedRectangleBorder(
              borderRadius: BorderRadius.all(Radius.circular(16)),
            ),
            backgroundColor: Colors.green[700],
            foregroundColor: Colors.white,
            elevation: 3,
            shadowColor: Colors.green[700],
          ),
        ),
      ),
      home: const Example(),
    );
  }
}

class Example extends StatelessWidget {
  const Example({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: DatePickerDialog(
          initialDate: DateTime.now(),
          firstDate: DateTime(2020),
          lastDate: DateTime(2030),
        ),
      ),
    );
  }
}
``` 

</details>

### Before 

Not possible to customize action buttons from the `DatePickerThemeData`.

### After 

![Screenshot 2023-08-18 at 16 42 00](https://github.com/flutter/flutter/assets/48603081/4ec01e93-c661-491d-9253-d687da8b76f3)

dev/tools/gen_defaults/lib/date_picker_template.dart

@@ -56,6 +56,16 @@ class _${blockName}DefaultsM3 extends DatePickerThemeData {
   @override
   Color? get backgroundColor => ${componentColor("md.comp.date-picker.modal.container")};
 
+  @override
+  ButtonStyle get cancelButtonStyle {
+    return TextButton.styleFrom();
+  }
+
+  @override
+  ButtonStyle get confirmButtonStyle {
+    return TextButton.styleFrom();
+  }
+
   @override
   Color? get shadowColor => ${colorOrTransparent("md.comp.date-picker.modal.container.shadow-color")};
 
@@ -231,8 +241,6 @@ class _${blockName}DefaultsM3 extends DatePickerThemeData {
 
   @override
   TextStyle? get rangePickerHeaderHelpStyle => ${textStyle("md.comp.date-picker.modal.range-selection.month.subhead")};
-
-
 }
 ''';
 }

packages/flutter/lib/src/material/date_picker.dart

@@ -543,6 +543,7 @@ class _DatePickerDialogState extends State<DatePickerDialog> with RestorationMix
         spacing: 8,
         children: <Widget>[
           TextButton(
+            style: datePickerTheme.cancelButtonStyle ?? defaults.cancelButtonStyle,
             onPressed: _handleCancel,
             child: Text(widget.cancelText ?? (
               useMaterial3
@@ -551,6 +552,7 @@ class _DatePickerDialogState extends State<DatePickerDialog> with RestorationMix
             )),
           ),
           TextButton(
+            style: datePickerTheme.confirmButtonStyle ?? defaults.confirmButtonStyle,
             onPressed: _handleOk,
             child: Text(widget.confirmText ?? localizations.okButtonLabel),
           ),

packages/flutter/lib/src/material/date_picker_theme.dart

@@ -7,10 +7,12 @@ import 'dart:ui' show lerpDouble;
 import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
 
+import 'button_style.dart';
 import 'color_scheme.dart';
 import 'colors.dart';
 import 'input_decorator.dart';
 import 'material_state.dart';
+import 'text_button.dart';
 import 'text_theme.dart';
 import 'theme.dart';
 
@@ -70,6 +72,8 @@ class DatePickerThemeData with Diagnosticable {
     this.rangeSelectionOverlayColor,
     this.dividerColor,
     this.inputDecorationTheme,
+    this.cancelButtonStyle,
+    this.confirmButtonStyle,
   });
 
   /// Overrides the default value of [Dialog.backgroundColor].
@@ -294,6 +298,12 @@ class DatePickerThemeData with Diagnosticable {
   /// If this is null, [ThemeData.inputDecorationTheme] is used instead.
   final InputDecorationTheme? inputDecorationTheme;
 
+  /// Overrides the default style of the cancel button of a [DatePickerDialog].
+  final ButtonStyle? cancelButtonStyle;
+
+  /// Overrrides the default style of the confirm (OK) button of a [DatePickerDialog].
+  final ButtonStyle? confirmButtonStyle;
+
   /// Creates a copy of this object with the given fields replaced with the
   /// new values.
   DatePickerThemeData copyWith({
@@ -331,6 +341,8 @@ class DatePickerThemeData with Diagnosticable {
     MaterialStateProperty<Color?>? rangeSelectionOverlayColor,
     Color? dividerColor,
     InputDecorationTheme? inputDecorationTheme,
+    ButtonStyle? cancelButtonStyle,
+    ButtonStyle? confirmButtonStyle,
   }) {
     return DatePickerThemeData(
       backgroundColor: backgroundColor ?? this.backgroundColor,
@@ -367,6 +379,8 @@ class DatePickerThemeData with Diagnosticable {
       rangeSelectionOverlayColor: rangeSelectionOverlayColor ?? this.rangeSelectionOverlayColor,
       dividerColor: dividerColor ?? this.dividerColor,
       inputDecorationTheme: inputDecorationTheme ?? this.inputDecorationTheme,
+      cancelButtonStyle: cancelButtonStyle ?? this.cancelButtonStyle,
+      confirmButtonStyle: confirmButtonStyle ?? this.confirmButtonStyle,
     );
   }
 
@@ -410,6 +424,8 @@ class DatePickerThemeData with Diagnosticable {
       rangeSelectionOverlayColor: MaterialStateProperty.lerp<Color?>(a?.rangeSelectionOverlayColor, b?.rangeSelectionOverlayColor, t, Color.lerp),
       dividerColor: Color.lerp(a?.dividerColor, b?.dividerColor, t),
       inputDecorationTheme: t < 0.5 ? a?.inputDecorationTheme : b?.inputDecorationTheme,
+      cancelButtonStyle: ButtonStyle.lerp(a?.cancelButtonStyle, b?.cancelButtonStyle, t),
+      confirmButtonStyle: ButtonStyle.lerp(a?.confirmButtonStyle, b?.confirmButtonStyle, t),
     );
   }
 
@@ -459,6 +475,8 @@ class DatePickerThemeData with Diagnosticable {
     rangeSelectionOverlayColor,
     dividerColor,
     inputDecorationTheme,
+    cancelButtonStyle,
+    confirmButtonStyle,
   ]);
 
   @override
@@ -500,7 +518,9 @@ class DatePickerThemeData with Diagnosticable {
       && other.rangeSelectionBackgroundColor == rangeSelectionBackgroundColor
       && other.rangeSelectionOverlayColor == rangeSelectionOverlayColor
       && other.dividerColor == dividerColor
-      && other.inputDecorationTheme == inputDecorationTheme;
+      && other.inputDecorationTheme == inputDecorationTheme
+      && other.cancelButtonStyle == cancelButtonStyle
+      && other.confirmButtonStyle == confirmButtonStyle;
   }
 
   @override
@@ -540,6 +560,8 @@ class DatePickerThemeData with Diagnosticable {
     properties.add(DiagnosticsProperty<MaterialStateProperty<Color?>>('rangeSelectionOverlayColor', rangeSelectionOverlayColor, defaultValue: null));
     properties.add(ColorProperty('dividerColor', dividerColor, defaultValue: null));
     properties.add(DiagnosticsProperty<InputDecorationTheme>('inputDecorationTheme', inputDecorationTheme, defaultValue: null));
+    properties.add(DiagnosticsProperty<ButtonStyle>('cancelButtonStyle', cancelButtonStyle, defaultValue: null));
+    properties.add(DiagnosticsProperty<ButtonStyle>('confirmButtonStyle', confirmButtonStyle, defaultValue: null));
   }
 }
 
@@ -658,6 +680,16 @@ class _DatePickerDefaultsM2 extends DatePickerThemeData {
   @override
   Color? get headerBackgroundColor => _isDark ? _colors.surface : _colors.primary;
 
+  @override
+  ButtonStyle get cancelButtonStyle {
+    return TextButton.styleFrom();
+  }
+
+  @override
+  ButtonStyle get confirmButtonStyle {
+    return TextButton.styleFrom();
+  }
+
   @override
   Color? get headerForegroundColor => _isDark ? _colors.onSurface : _colors.onPrimary;
 
@@ -818,6 +850,16 @@ class _DatePickerDefaultsM3 extends DatePickerThemeData {
   @override
   Color? get backgroundColor => _colors.surface;
 
+  @override
+  ButtonStyle get cancelButtonStyle {
+    return TextButton.styleFrom();
+  }
+
+  @override
+  ButtonStyle get confirmButtonStyle {
+    return TextButton.styleFrom();
+  }
+
   @override
   Color? get shadowColor => Colors.transparent;
 
@@ -993,8 +1035,6 @@ class _DatePickerDefaultsM3 extends DatePickerThemeData {
 
   @override
   TextStyle? get rangePickerHeaderHelpStyle => _textTheme.titleSmall;
-
-
 }
 
 // END GENERATED TOKEN PROPERTIES - DatePicker

packages/flutter/test/material/date_picker_theme_test.dart

@@ -46,7 +46,9 @@ void main() {
     inputDecorationTheme: InputDecorationTheme(
       fillColor: Color(0xffffff5f),
       border: UnderlineInputBorder(),
-    )
+    ),
+    cancelButtonStyle: ButtonStyle(foregroundColor: MaterialStatePropertyAll<Color>(Color(0xffffff6f))),
+    confirmButtonStyle: ButtonStyle(foregroundColor: MaterialStatePropertyAll<Color>(Color(0xffffff7f))),
   );
 
   Material findDialogMaterial(WidgetTester tester) {
@@ -77,6 +79,10 @@ void main() {
     return container.decoration as BoxDecoration?;
   }
 
+  ButtonStyle actionButtonStyle(WidgetTester tester, String text) {
+    return tester.widget<TextButton>(find.widgetWithText(TextButton, text)).style!;
+  }
+
   const Size wideWindowSize = Size(1920.0, 1080.0);
   const Size narrowWindowSize = Size(1070.0, 1770.0);
 
@@ -126,6 +132,8 @@ void main() {
     expect(theme.rangeSelectionOverlayColor, null);
     expect(theme.dividerColor, null);
     expect(theme.inputDecorationTheme, null);
+    expect(theme.cancelButtonStyle, null);
+    expect(theme.confirmButtonStyle, null);
   });
 
   testWidgets('DatePickerTheme.defaults M3 defaults', (WidgetTester tester) async {
@@ -201,6 +209,8 @@ void main() {
     expect(m3.rangePickerHeaderHelpStyle, textTheme.titleSmall);
     expect(m3.dividerColor, null);
     expect(m3.inputDecorationTheme, null);
+    expect(m3.cancelButtonStyle.toString(), equalsIgnoringHashCodes(TextButton.styleFrom().toString()));
+    expect(m3.confirmButtonStyle.toString(), equalsIgnoringHashCodes(TextButton.styleFrom().toString()));
   });
 
   testWidgets('DatePickerTheme.defaults M2 defaults', (WidgetTester tester) async {
@@ -268,6 +278,8 @@ void main() {
     expect(m2.rangePickerHeaderHelpStyle, textTheme.labelSmall);
     expect(m2.dividerColor, null);
     expect(m2.inputDecorationTheme, null);
+    expect(m2.cancelButtonStyle.toString(), equalsIgnoringHashCodes(TextButton.styleFrom().toString()));
+    expect(m2.confirmButtonStyle.toString(), equalsIgnoringHashCodes(TextButton.styleFrom().toString()));
   });
 
   testWidgets('Default DatePickerThemeData debugFillProperties', (WidgetTester tester) async {
@@ -292,9 +304,7 @@ void main() {
         .map((DiagnosticsNode node) => node.toString())
         .toList();
 
-    expect(
-      description,
-      equalsIgnoringHashCodes(<String>[
+    expect(description, equalsIgnoringHashCodes(<String>[
       'backgroundColor: Color(0xfffffff0)',
       'elevation: 6.0',
       'shadowColor: Color(0xfffffff1)',
@@ -328,9 +338,10 @@ void main() {
       'rangeSelectionBackgroundColor: Color(0xffffff2f)',
       'rangeSelectionOverlayColor: MaterialStatePropertyAll(Color(0xffffff3f))',
       'dividerColor: Color(0xffffff4f)',
-      'inputDecorationTheme: InputDecorationTheme#00000(fillColor: Color(0xffffff5f), border: UnderlineInputBorder())'
-      ]),
-    );
+      'inputDecorationTheme: InputDecorationTheme#00000(fillColor: Color(0xffffff5f), border: UnderlineInputBorder())',
+      'cancelButtonStyle: ButtonStyle#00000(foregroundColor: MaterialStatePropertyAll(Color(0xffffff6f)))',
+      'confirmButtonStyle: ButtonStyle#00000(foregroundColor: MaterialStatePropertyAll(Color(0xffffff7f)))'
+    ]));
   });
 
   testWidgets('DatePickerDialog uses ThemeData datePicker theme (calendar mode)', (WidgetTester tester) async {
@@ -426,6 +437,12 @@ void main() {
     await gesture.moveTo(tester.getCenter(find.text('2024')));
     await tester.pumpAndSettle();
     expect(inkFeatures, paints..rect(color: datePickerTheme.yearOverlayColor?.resolve(<MaterialState>{})));
+
+    final ButtonStyle cancelButtonStyle = actionButtonStyle(tester, 'Cancel');
+    expect(cancelButtonStyle.toString(), equalsIgnoringHashCodes(datePickerTheme.cancelButtonStyle.toString()));
+
+    final ButtonStyle confirmButtonStyle = actionButtonStyle(tester, 'OK');
+    expect(confirmButtonStyle.toString(), equalsIgnoringHashCodes(datePickerTheme.confirmButtonStyle.toString()));
   });
 
   testWidgets('DatePickerDialog uses ThemeData datePicker theme (input mode)', (WidgetTester tester) async {
@@ -467,6 +484,12 @@ void main() {
 
     final InputDecoration inputDecoration = tester.widget<TextField>(find.byType(TextField)).decoration!;
     expect(inputDecoration.fillColor, datePickerTheme.inputDecorationTheme?.fillColor);
+
+    final ButtonStyle cancelButtonStyle = actionButtonStyle(tester, 'Cancel');
+    expect(cancelButtonStyle.toString(), equalsIgnoringHashCodes(datePickerTheme.cancelButtonStyle.toString()));
+
+    final ButtonStyle confirmButtonStyle = actionButtonStyle(tester, 'OK');
+    expect(confirmButtonStyle.toString(), equalsIgnoringHashCodes(datePickerTheme.confirmButtonStyle.toString()));
   });
 
   testWidgets('DateRangePickerDialog uses ThemeData datePicker theme', (WidgetTester tester) async {