fix(flutter): 优化二级页面返回按钮样式

test/drama_detail/drama_detail_view_test.dart

@@ -58,6 +58,21 @@ void main() {
       tester.getSize(find.byKey(const Key('detail-poster'))),
       const Size(96, 128),
     );
+    expect(
+      tester.getSize(find.byKey(const Key('detail-back'))),
+      const Size(40, 40),
+    );
+    expect(
+      tester
+          .widget<Material>(
+            find.descendant(
+              of: find.byKey(const Key('detail-back')),
+              matching: find.byType(Material),
+            ),
+          )
+          .color,
+      const Color(0x59000000),
+    );
     expect(
       tester
           .widget<Text>(find.byKey(const Key('detail-title')))