Fix `CalendarDatePicker` day selection shape and overlay (#144317)

fixes [`DatePickerDialog` date entry hover background and ink splash have different radius](https://github.com/flutter/flutter/issues/141350)
fixes [Ability to customize DatePicker day selection background and overlay shape](https://github.com/flutter/flutter/issues/144220)

### 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(
      home: Scaffold(
        body: Center(
          child: Builder(builder: (context) {
            return FilledButton(
              onPressed: () {
                showDatePicker(
                  context: context,
                  initialDate: DateTime.now(),
                  firstDate: DateTime.utc(2010),
                  lastDate: DateTime.utc(2030),
                );
              },
              child: const Text('Show Date picker'),
            );
          }),
        ),
      ),
    );
  }
}
```

</details>

### Material DatePicker states specs

![overlay_specs](https://github.com/flutter/flutter/assets/48603081/45ce16cf-7ee9-41e1-a4fa-327de07b78d1)

### Day selection overlay

| Before | After |
| --------------- | --------------- |
| <img src="https://github.com/flutter/flutter/assets/48603081/b529d38d-0232-494b-8bf2-55d28420a245" /> | <img src="https://github.com/flutter/flutter/assets/48603081/c4799559-a7ef-45fd-aed9-aeb386370580"  /> |

### Hover, pressed, highlight preview

| Before | After |
| --------------- | --------------- |
| <video src="https://github.com/flutter/flutter/assets/48603081/8edde82a-7f39-4482-afab-183e1bce5991" /> | <video src="https://github.com/flutter/flutter/assets/48603081/04e1502e-67a4-4b33-973d-463067d70151" /> |

### Using `DatePickerThemeData.dayShape` to customize day selection background and overlay shape

| Before | After |
| --------------- | --------------- |
| <img src="https://github.com/flutter/flutter/assets/48603081/a0c85f58-a69b-4e14-a45d-41e580ceedce"  />  | <img src="https://github.com/flutter/flutter/assets/48603081/db67cee1-d28d-4168-98b8-fd7a9cb70cda" /> | 

### Example preview

![Screenshot 2024-02-29 at 15 07 50](https://github.com/flutter/flutter/assets/48603081/3770ed5c-28bf-4d0a-9514-87e1cd2ce515)

dev/tools/gen_defaults/lib/date_picker_template.dart

@@ -44,6 +44,9 @@ class _${blockName}DefaultsM3 extends DatePickerThemeData {
     : super(
         elevation: ${elevation("md.comp.date-picker.modal.container")},
         shape: ${shape("md.comp.date-picker.modal.container")},
+        // TODO(tahatesser): Update this to use token when gen_defaults
+        // supports `CircleBorder` for fully rounded corners.
+        dayShape: const MaterialStatePropertyAll<OutlinedBorder>(CircleBorder()),
         rangePickerElevation: ${elevation("md.comp.date-picker.modal.range-selection.container")},
         rangePickerShape: ${shape("md.comp.date-picker.modal.range-selection.container")},
       );

examples/api/lib/material/date_picker/date_picker_theme_day_shape.0.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+
+/// Flutter code sample for [DatePickerThemeData].
+
+void main() => runApp(const DatePickerApp());
+
+class DatePickerApp extends StatelessWidget {
+  const DatePickerApp({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      theme: ThemeData(
+        datePickerTheme: DatePickerThemeData(
+          todayBackgroundColor: const MaterialStatePropertyAll<Color>(Colors.amber),
+          todayForegroundColor: const MaterialStatePropertyAll<Color>(Colors.black),
+          todayBorder: const BorderSide(width: 2),
+          dayShape: MaterialStatePropertyAll<OutlinedBorder>(
+            RoundedRectangleBorder(
+              borderRadius: BorderRadius.circular(8.0),
+            ),
+          ),
+          shape: RoundedRectangleBorder(
+            borderRadius: BorderRadius.circular(16.0),
+          ),
+        ),
+      ),
+      home: const DatePickerExample(),
+    );
+  }
+}
+
+class DatePickerExample extends StatefulWidget {
+  const DatePickerExample({super.key});
+
+  @override
+  State<DatePickerExample> createState() => _DatePickerExampleState();
+}
+
+class _DatePickerExampleState extends State<DatePickerExample> {
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      body: Center(
+        child: OutlinedButton(
+          onPressed: () {
+            showDatePicker(
+              context: context,
+              initialDate: DateTime(2021, 1, 20),
+              currentDate: DateTime(2021, 1, 15),
+              firstDate: DateTime(2021),
+              lastDate: DateTime(2022),
+            );
+          },
+          child: const Text('Open Date Picker'),
+        ),
+      ),
+    );
+  }
+}

examples/api/test/material/date_picker/date_picker_theme_day_shape.0_test.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+import 'package:flutter_api_samples/material/date_picker/date_picker_theme_day_shape.0.dart' as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('DatePickerThemeData.dayShape updates day selection shape decoration', (WidgetTester tester) async {
+    final ThemeData theme = ThemeData();
+    final OutlinedBorder dayShape = RoundedRectangleBorder(borderRadius: BorderRadius.circular(8.0));
+    const Color todayBackgroundColor = Colors.amber;
+    const Color todayForegroundColor = Colors.black;
+    const BorderSide todayBorder = BorderSide(width: 2);
+
+    await tester.pumpWidget(
+      const example.DatePickerApp(),
+    );
+
+    await tester.tap(find.text('Open Date Picker'));
+    await tester.pumpAndSettle();
+
+    ShapeDecoration dayShapeDecoration = tester.widget<DecoratedBox>(find.ancestor(
+      of: find.text('15'),
+      matching: find.byType(DecoratedBox),
+    )).decoration as ShapeDecoration;
+
+    // Test the current day shape decoration.
+    expect(dayShapeDecoration.color, todayBackgroundColor);
+    expect(dayShapeDecoration.shape, dayShape.copyWith(side: todayBorder.copyWith(color: todayForegroundColor)));
+
+    dayShapeDecoration = tester.widget<DecoratedBox>(find.ancestor(
+      of: find.text('20'),
+      matching: find.byType(DecoratedBox),
+    )).decoration as ShapeDecoration;
+
+    // Test the selected day shape decoration.
+    expect(dayShapeDecoration.color, theme.colorScheme.primary);
+    expect(dayShapeDecoration.shape, dayShape);
+
+    // Tap to select current day as the selected day.
+    await tester.tap(find.text('15'));
+    await tester.pumpAndSettle();
+
+    dayShapeDecoration = tester.widget<DecoratedBox>(find.ancestor(
+      of: find.text('15'),
+      matching: find.byType(DecoratedBox),
+    )).decoration as ShapeDecoration;
+
+    // Test the selected day shape decoration.
+    expect(dayShapeDecoration.color, todayBackgroundColor);
+    expect(dayShapeDecoration.shape, dayShape.copyWith(side: todayBorder.copyWith(color: todayForegroundColor)));
+  });
+}

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

@@ -1057,21 +1057,21 @@ class _DayState extends State<_Day> {
     final MaterialStateProperty<Color?> dayOverlayColor = MaterialStateProperty.resolveWith<Color?>(
       (Set<MaterialState> states) => effectiveValue((DatePickerThemeData? theme) => theme?.dayOverlayColor?.resolve(states)),
     );
-    final BoxDecoration decoration = widget.isToday
-      ? BoxDecoration(
+    final OutlinedBorder dayShape = resolve<OutlinedBorder?>((DatePickerThemeData? theme) => theme?.dayShape, states)!;
+    final ShapeDecoration decoration = widget.isToday
+      ? ShapeDecoration(
           color: dayBackgroundColor,
-          border: Border.fromBorderSide(
-            (datePickerTheme.todayBorder ?? defaults.todayBorder!)
-              .copyWith(color: dayForegroundColor)
+          shape: dayShape.copyWith(
+            side: (datePickerTheme.todayBorder ?? defaults.todayBorder!)
+              .copyWith(color: dayForegroundColor),
           ),
-          shape: BoxShape.circle,
         )
-      : BoxDecoration(
+      : ShapeDecoration(
           color: dayBackgroundColor,
-          shape: BoxShape.circle,
+          shape: dayShape,
         );
 
-    Widget dayWidget = Container(
+    Widget dayWidget = DecoratedBox(
       decoration: decoration,
       child: Center(
         child: Text(localizations.formatDecimal(widget.day.day), style: dayStyle?.apply(color: dayForegroundColor)),
@@ -1086,9 +1086,10 @@ class _DayState extends State<_Day> {
       dayWidget = InkResponse(
         focusNode: widget.focusNode,
         onTap: () => widget.onChanged(widget.day),
-        radius: _dayPickerRowHeight / 2 + 4,
         statesController: _statesController,
         overlayColor: dayOverlayColor,
+        customBorder: dayShape,
+        containedInkWell: true,
         child: Semantics(
           // We want the day of month to be spoken first irrespective of the
           // locale-specific preferences or TextDirection. This is because

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

@@ -52,6 +52,7 @@ class DatePickerThemeData with Diagnosticable {
     this.dayForegroundColor,
     this.dayBackgroundColor,
     this.dayOverlayColor,
+    this.dayShape,
     this.todayForegroundColor,
     this.todayBackgroundColor,
     this.todayBorder,
@@ -163,12 +164,41 @@ class DatePickerThemeData with Diagnosticable {
   /// indicate that a day in the grid is focused, hovered, or pressed.
   final MaterialStateProperty<Color?>? dayOverlayColor;
 
+  /// Overrides the default shape used to paint the shape decoration of the
+  /// day labels in the grid of the date picker.
+  ///
+  /// If the selected day is the current day, the provided shape with the
+  /// value of [todayBackgroundColor] is used to paint the shape decoration of
+  /// the day label and the value of [todayBorder] and [todayForegroundColor] is
+  /// used to paint the border.
+  ///
+  /// If the selected day is not the current day, the provided shape with the
+  /// value of [dayBackgroundColor] is used to paint the shape decoration of
+  /// the day label.
+  ///
+  /// {@tool dartpad}
+  /// This sample demonstrates how to customize the day selector shape decoration
+  /// using the [dayShape], [todayForegroundColor], [todayBackgroundColor], and
+  /// [todayBorder] properties.
+  ///
+  /// ** See code in examples/api/lib/material/date_picker/date_picker_theme_day_shape.0.dart **
+  /// {@end-tool}
+  final MaterialStateProperty<OutlinedBorder?>? dayShape;
+
   /// Overrides the default color used to paint the
   /// [DatePickerDialog.currentDate] label in the grid of the dialog's
   /// [CalendarDatePicker] and the corresponding year in the dialog's
   /// [YearPicker].
   ///
   /// This will be used instead of the [TextStyle.color] provided in [dayStyle].
+  ///
+  /// {@tool dartpad}
+  /// This sample demonstrates how to customize the day selector shape decoration
+  /// using the [dayShape], [todayForegroundColor], [todayBackgroundColor], and
+  /// [todayBorder] properties.
+  ///
+  /// ** See code in examples/api/lib/material/date_picker/date_picker_theme_day_shape.0.dart **
+  /// {@end-tool}
   final MaterialStateProperty<Color?>? todayForegroundColor;
 
   /// Overrides the default color used to paint the background of the
@@ -181,6 +211,14 @@ class DatePickerThemeData with Diagnosticable {
   ///
   /// The border side's [BorderSide.color] is not used,
   /// [todayForegroundColor] is used instead.
+  ///
+  /// {@tool dartpad}
+  /// This sample demonstrates how to customize the day selector shape decoration
+  /// using the [dayShape], [todayForegroundColor], [todayBackgroundColor], and
+  /// [todayBorder] properties.
+  ///
+  /// ** See code in examples/api/lib/material/date_picker/date_picker_theme_day_shape.0.dart **
+  /// {@end-tool}
   final BorderSide? todayBorder;
 
   /// Overrides the default text style used to paint each of the year
@@ -326,6 +364,7 @@ class DatePickerThemeData with Diagnosticable {
     MaterialStateProperty<Color?>? dayForegroundColor,
     MaterialStateProperty<Color?>? dayBackgroundColor,
     MaterialStateProperty<Color?>? dayOverlayColor,
+    MaterialStateProperty<OutlinedBorder?>? dayShape,
     MaterialStateProperty<Color?>? todayForegroundColor,
     MaterialStateProperty<Color?>? todayBackgroundColor,
     BorderSide? todayBorder,
@@ -364,6 +403,7 @@ class DatePickerThemeData with Diagnosticable {
       dayForegroundColor: dayForegroundColor ?? this.dayForegroundColor,
       dayBackgroundColor: dayBackgroundColor ?? this.dayBackgroundColor,
       dayOverlayColor: dayOverlayColor ?? this.dayOverlayColor,
+      dayShape: dayShape ?? this.dayShape,
       todayForegroundColor: todayForegroundColor ?? this.todayForegroundColor,
       todayBackgroundColor: todayBackgroundColor ?? this.todayBackgroundColor,
       todayBorder: todayBorder ?? this.todayBorder,
@@ -409,6 +449,7 @@ class DatePickerThemeData with Diagnosticable {
       dayForegroundColor: MaterialStateProperty.lerp<Color?>(a?.dayForegroundColor, b?.dayForegroundColor, t, Color.lerp),
       dayBackgroundColor: MaterialStateProperty.lerp<Color?>(a?.dayBackgroundColor, b?.dayBackgroundColor, t, Color.lerp),
       dayOverlayColor: MaterialStateProperty.lerp<Color?>(a?.dayOverlayColor, b?.dayOverlayColor, t, Color.lerp),
+      dayShape: MaterialStateProperty.lerp<OutlinedBorder?>(a?.dayShape, b?.dayShape, t, OutlinedBorder.lerp),
       todayForegroundColor: MaterialStateProperty.lerp<Color?>(a?.todayForegroundColor, b?.todayForegroundColor, t, Color.lerp),
       todayBackgroundColor: MaterialStateProperty.lerp<Color?>(a?.todayBackgroundColor, b?.todayBackgroundColor, t, Color.lerp),
       todayBorder: _lerpBorderSide(a?.todayBorder, b?.todayBorder, t),
@@ -460,6 +501,7 @@ class DatePickerThemeData with Diagnosticable {
     dayForegroundColor,
     dayBackgroundColor,
     dayOverlayColor,
+    dayShape,
     todayForegroundColor,
     todayBackgroundColor,
     todayBorder,
@@ -504,6 +546,7 @@ class DatePickerThemeData with Diagnosticable {
       && other.dayForegroundColor == dayForegroundColor
       && other.dayBackgroundColor == dayBackgroundColor
       && other.dayOverlayColor == dayOverlayColor
+      && other.dayShape == dayShape
       && other.todayForegroundColor == todayForegroundColor
       && other.todayBackgroundColor == todayBackgroundColor
       && other.todayBorder == todayBorder
@@ -545,6 +588,7 @@ class DatePickerThemeData with Diagnosticable {
     properties.add(DiagnosticsProperty<MaterialStateProperty<Color?>>('dayForegroundColor', dayForegroundColor, defaultValue: null));
     properties.add(DiagnosticsProperty<MaterialStateProperty<Color?>>('dayBackgroundColor', dayBackgroundColor, defaultValue: null));
     properties.add(DiagnosticsProperty<MaterialStateProperty<Color?>>('dayOverlayColor', dayOverlayColor, defaultValue: null));
+    properties.add(DiagnosticsProperty<MaterialStateProperty<OutlinedBorder?>>('dayShape', dayShape, defaultValue: null));
     properties.add(DiagnosticsProperty<MaterialStateProperty<Color?>>('todayForegroundColor', todayForegroundColor, defaultValue: null));
     properties.add(DiagnosticsProperty<MaterialStateProperty<Color?>>('todayBackgroundColor', todayBackgroundColor, defaultValue: null));
     properties.add(DiagnosticsProperty<BorderSide?>('todayBorder', todayBorder, defaultValue: null));
@@ -672,6 +716,7 @@ class _DatePickerDefaultsM2 extends DatePickerThemeData {
     : super(
         elevation: 24.0,
         shape: const RoundedRectangleBorder(borderRadius: BorderRadius.all(Radius.circular(4.0))),
+        dayShape: const MaterialStatePropertyAll<OutlinedBorder>(CircleBorder()),
         rangePickerElevation: 0.0,
         rangePickerShape: const RoundedRectangleBorder(),
       );
@@ -843,6 +888,9 @@ class _DatePickerDefaultsM3 extends DatePickerThemeData {
     : super(
         elevation: 6.0,
         shape: const RoundedRectangleBorder(borderRadius: BorderRadius.all(Radius.circular(28.0))),
+        // TODO(tahatesser): Update this to use token when gen_defaults
+        // supports `CircleBorder` for fully rounded corners.
+        dayShape: const MaterialStatePropertyAll<OutlinedBorder>(CircleBorder()),
         rangePickerElevation: 0.0,
         rangePickerShape: const RoundedRectangleBorder(),
       );

packages/flutter/test/material/calendar_date_picker_test.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -25,10 +26,11 @@ void main() {
     DatePickerMode initialCalendarMode = DatePickerMode.day,
     SelectableDayPredicate? selectableDayPredicate,
     TextDirection textDirection = TextDirection.ltr,
+    ThemeData? theme,
     bool? useMaterial3,
   }) {
     return MaterialApp(
-      theme: ThemeData(useMaterial3: useMaterial3),
+      theme: theme ?? ThemeData(useMaterial3: useMaterial3),
       home: Material(
         child: Directionality(
           textDirection: textDirection,
@@ -1132,6 +1134,43 @@ void main() {
         semantics.dispose();
       }, variant: TargetPlatformVariant.desktop());
     });
+
+    // This is a regression test for https://github.com/flutter/flutter/issues/141350.
+    testWidgets('Default day selection overlay', (WidgetTester tester) async {
+      final ThemeData theme = ThemeData();
+      await tester.pumpWidget(calendarDatePicker(
+        firstDate: DateTime(2016, DateTime.december, 15),
+        initialDate: DateTime(2017, DateTime.january, 15),
+        lastDate: DateTime(2017, DateTime.february, 15),
+        onDisplayedMonthChanged: (DateTime date) {},
+        theme: theme,
+      ));
+
+      RenderObject inkFeatures = tester.allRenderObjects.firstWhere((RenderObject object) => object.runtimeType.toString() == '_RenderInkFeatures');
+      expect(inkFeatures, isNot(paints..circle(radius: 35.0, color: theme.colorScheme.onSurfaceVariant.withOpacity(0.08))));
+      expect(inkFeatures, paintsExactlyCountTimes(#clipPath, 0));
+
+      final TestGesture gesture = await tester.createGesture(
+        kind: PointerDeviceKind.mouse,
+      );
+      await gesture.addPointer();
+      await gesture.moveTo(tester.getCenter(find.text('25')));
+      await tester.pumpAndSettle();
+      inkFeatures = tester.allRenderObjects.firstWhere((RenderObject object) => object.runtimeType.toString() == '_RenderInkFeatures');
+      expect(inkFeatures, paints..circle(radius: 35.0, color: theme.colorScheme.onSurfaceVariant.withOpacity(0.08)));
+      expect(inkFeatures, paintsExactlyCountTimes(#clipPath, 1));
+
+      final Rect expectedClipRect = Rect.fromCircle(center: const Offset(400.0, 241.0), radius: 35.0);
+      final Path expectedClipPath = Path()..addRect(expectedClipRect);
+      expect(
+        inkFeatures,
+        paints..clipPath(pathMatcher: coversSameAreaAs(
+          expectedClipPath,
+          areaToCompare: expectedClipRect,
+          sampleSize: 100,
+        )),
+      );
+    });
   });
 
   group('YearPicker', () {

packages/flutter/test/material/date_picker_theme_test.dart

@@ -24,6 +24,7 @@ void main() {
     dayForegroundColor: MaterialStatePropertyAll<Color>(Color(0xfffffff5)),
     dayBackgroundColor: MaterialStatePropertyAll<Color>(Color(0xfffffff6)),
     dayOverlayColor: MaterialStatePropertyAll<Color>(Color(0xfffffff7)),
+    dayShape: MaterialStatePropertyAll<OutlinedBorder>(RoundedRectangleBorder()),
     todayForegroundColor: MaterialStatePropertyAll<Color>(Color(0xfffffff8)),
     todayBackgroundColor: MaterialStatePropertyAll<Color>(Color(0xfffffff9)),
     todayBorder: BorderSide(width: 3),
@@ -79,6 +80,15 @@ void main() {
     return container.decoration as BoxDecoration?;
   }
 
+  ShapeDecoration? findDayDecoration(WidgetTester tester, String day) {
+    return tester.widget<DecoratedBox>(
+      find.ancestor(
+        of: find.text(day),
+        matching: find.byType(DecoratedBox)
+      ),
+    ).decoration as ShapeDecoration?;
+  }
+
   ButtonStyle actionButtonStyle(WidgetTester tester, String text) {
     return tester.widget<TextButton>(find.widgetWithText(TextButton, text)).style!;
   }
@@ -112,6 +122,7 @@ void main() {
     expect(theme.dayForegroundColor, null);
     expect(theme.dayBackgroundColor, null);
     expect(theme.dayOverlayColor, null);
+    expect(theme.dayShape, null);
     expect(theme.todayForegroundColor, null);
     expect(theme.todayBackgroundColor, null);
     expect(theme.todayBorder, null);
@@ -183,6 +194,7 @@ void main() {
     expect(m3.dayOverlayColor?.resolve(<MaterialState>{MaterialState.selected, MaterialState.hovered, MaterialState.pressed}), colorScheme.onPrimary.withOpacity(0.1));
     expect(m3.dayOverlayColor?.resolve(<MaterialState>{MaterialState.hovered, MaterialState.focused}), colorScheme.onSurfaceVariant.withOpacity(0.08));
     expect(m3.dayOverlayColor?.resolve(<MaterialState>{MaterialState.hovered, MaterialState.pressed}), colorScheme.onSurfaceVariant.withOpacity(0.1));
+    expect(m3.dayShape?.resolve(<MaterialState>{}), const CircleBorder());
     expect(m3.todayForegroundColor?.resolve(<MaterialState>{}), colorScheme.primary);
     expect(m3.todayForegroundColor?.resolve(<MaterialState>{MaterialState.disabled}), colorScheme.primary.withOpacity(0.38));
     expect(m3.todayBorder, BorderSide(color: colorScheme.primary));
@@ -256,6 +268,7 @@ void main() {
     expect(m2.dayOverlayColor?.resolve(<MaterialState>{MaterialState.hovered}), colorScheme.onSurfaceVariant.withOpacity(0.08));
     expect(m2.dayOverlayColor?.resolve(<MaterialState>{MaterialState.focused}), colorScheme.onSurfaceVariant.withOpacity(0.12));
     expect(m2.dayOverlayColor?.resolve(<MaterialState>{MaterialState.pressed}), colorScheme.onSurfaceVariant.withOpacity(0.12));
+    expect(m2.dayShape?.resolve(<MaterialState>{}), const CircleBorder());
     expect(m2.todayForegroundColor?.resolve(<MaterialState>{}), colorScheme.primary);
     expect(m2.todayForegroundColor?.resolve(<MaterialState>{MaterialState.disabled}), colorScheme.onSurface.withOpacity(0.38));
     expect(m2.todayBorder, BorderSide(color: colorScheme.primary));
@@ -319,6 +332,7 @@ void main() {
       'dayForegroundColor: MaterialStatePropertyAll(Color(0xfffffff5))',
       'dayBackgroundColor: MaterialStatePropertyAll(Color(0xfffffff6))',
       'dayOverlayColor: MaterialStatePropertyAll(Color(0xfffffff7))',
+      'dayShape: MaterialStatePropertyAll(RoundedRectangleBorder(BorderSide(width: 0.0, style: none), BorderRadius.zero))',
       'todayForegroundColor: MaterialStatePropertyAll(Color(0xfffffff8))',
       'todayBackgroundColor: MaterialStatePropertyAll(Color(0xfffffff9))',
       'todayBorder: BorderSide(width: 3.0)',
@@ -389,18 +403,24 @@ void main() {
     expect(selectedDate.style?.fontSize, datePickerTheme.headerHeadlineStyle?.fontSize);
 
     final Text day31 = tester.widget<Text>(find.text('31'));
-    final BoxDecoration day31Decoration = findTextDecoration(tester, '31')!;
+    final ShapeDecoration day31Decoration = findDayDecoration(tester, '31')!;
     expect(day31.style?.color, datePickerTheme.dayForegroundColor?.resolve(<MaterialState>{}));
     expect(day31.style?.fontSize, datePickerTheme.dayStyle?.fontSize);
     expect(day31Decoration.color, datePickerTheme.dayBackgroundColor?.resolve(<MaterialState>{}));
+    expect(day31Decoration.shape, datePickerTheme.dayShape?.resolve(<MaterialState>{}));
 
     final Text day24 = tester.widget<Text>(find.text('24')); // DatePickerDialog.currentDate
-    final BoxDecoration day24Decoration = findTextDecoration(tester, '24')!;
+    final ShapeDecoration day24Decoration = findDayDecoration(tester, '24')!;
+    final OutlinedBorder day24Shape = day24Decoration.shape as OutlinedBorder;
     expect(day24.style?.fontSize, datePickerTheme.dayStyle?.fontSize);
     expect(day24.style?.color, datePickerTheme.todayForegroundColor?.resolve(<MaterialState>{}));
     expect(day24Decoration.color, datePickerTheme.todayBackgroundColor?.resolve(<MaterialState>{}));
-    expect(day24Decoration.border?.top.width, datePickerTheme.todayBorder?.width);
-    expect(day24Decoration.border?.bottom.width, datePickerTheme.todayBorder?.width);
+    expect(
+      day24Decoration.shape,
+      datePickerTheme.dayShape?.resolve(<MaterialState>{})!
+        .copyWith(side: datePickerTheme.todayBorder?.copyWith(color: datePickerTheme.todayForegroundColor?.resolve(<MaterialState>{}))),
+    );
+    expect(day24Shape.side.width, datePickerTheme.todayBorder?.width);
 
     // Test the day overlay color.
     final RenderObject inkFeatures = tester.allRenderObjects.firstWhere((RenderObject object) => object.runtimeType.toString() == '_RenderInkFeatures');