refactor tabbar: Homepage adaptation

1. remove redundant MaterialApp in GetMaterialApp
2. unified background color

Signed-off-by: 21pages <pages21@163.com>

flutter/lib/desktop/pages/desktop_setting_page.dart

@@ -0,0 +1,15 @@
+import 'package:flutter/cupertino.dart';
+
+class DesktopSettingPage extends StatefulWidget {
+  DesktopSettingPage({Key? key}) : super(key: key);
+
+  @override
+  State<DesktopSettingPage> createState() => _DesktopSettingPageState();
+}
+
+class _DesktopSettingPageState extends State<DesktopSettingPage> {
+  @override
+  Widget build(BuildContext context) {
+    return Text("Settings");
+  }
+}