Let text selection toolbar buttons be independent from theme (#27573)

packages/flutter/lib/src/cupertino/text_selection.dart

@@ -8,6 +8,7 @@ import 'package:flutter/widgets.dart';
 import 'package:flutter/rendering.dart';
 
 import 'button.dart';
+import 'colors.dart';
 import 'localizations.dart';
 
 // Padding around the line at the edge of the text selection that has 0 width and
@@ -33,9 +34,11 @@ const EdgeInsets _kToolbarButtonPadding = EdgeInsets.symmetric(vertical: 10.0, h
 const BorderRadius _kToolbarBorderRadius = BorderRadius.all(Radius.circular(7.5));
 
 const TextStyle _kToolbarButtonFontStyle = TextStyle(
+  inherit: false,
   fontSize: 14.0,
   letterSpacing: -0.11,
   fontWeight: FontWeight.w300,
+  color: CupertinoColors.white,
 );
 
 /// Paints a triangle below the toolbar.
@@ -113,8 +116,12 @@ class _TextSelectionToolbar extends StatelessWidget {
         ClipRRect(
           borderRadius: _kToolbarBorderRadius,
           child: DecoratedBox(
-            decoration: const BoxDecoration(
+            decoration: BoxDecoration(
               color: _kToolbarDividerColor,
+              borderRadius: _kToolbarBorderRadius,
+              // Add a hairline border with the button color to avoid
+              // antialiasing artifacts.
+              border: Border.all(color: _kToolbarBackgroundColor, width: 0),
             ),
             child: Row(mainAxisSize: MainAxisSize.min, children: items),
           ),

packages/flutter/test/cupertino/text_field_test.dart

@@ -702,6 +702,68 @@ void main() {
     expect(controller.text, 'abcdef');
   });
 
+  testWidgets('toolbar has the same visual regardless of theming', (WidgetTester tester) async {
+    final TextEditingController controller = TextEditingController(
+      text: "j'aime la poutine",
+    );
+
+    await tester.pumpWidget(
+      CupertinoApp(
+        home: Column(
+          children: <Widget>[
+            CupertinoTextField(
+              controller: controller,
+            ),
+          ],
+        ),
+      ),
+    );
+
+    await tester.longPressAt(
+      tester.getTopRight(find.text("j'aime la poutine"))
+    );
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 200));
+
+    Text text = tester.widget<Text>(find.text('Paste'));
+    expect(text.style.color, CupertinoColors.white);
+    expect(text.style.fontSize, 14);
+    expect(text.style.letterSpacing, -0.11);
+    expect(text.style.fontWeight, FontWeight.w300);
+
+    // Change the theme.
+    await tester.pumpWidget(
+      CupertinoApp(
+        theme: const CupertinoThemeData(
+          brightness: Brightness.dark,
+          textTheme: CupertinoTextThemeData(
+            textStyle: TextStyle(fontSize: 100, fontWeight: FontWeight.w800),
+          ),
+        ),
+        home: Column(
+          children: <Widget>[
+            CupertinoTextField(
+              controller: controller,
+            ),
+          ],
+        ),
+      ),
+    );
+
+    await tester.longPressAt(
+      tester.getTopRight(find.text("j'aime la poutine"))
+    );
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 200));
+
+    text = tester.widget<Text>(find.text('Paste'));
+    // The toolbar buttons' text are still the same style.
+    expect(text.style.color, CupertinoColors.white);
+    expect(text.style.fontSize, 14);
+    expect(text.style.letterSpacing, -0.11);
+    expect(text.style.fontWeight, FontWeight.w300);
+  });
+
   testWidgets('copy paste', (WidgetTester tester) async {
     await tester.pumpWidget(
       CupertinoApp(