add dart tag

@@ -58,7 +58,7 @@ class MyApp extends StatelessWidget {
 }
 }
 ```
 ```
 The second way:Does not support the use of font adaptation in the App
 The second way:Does not support the use of font adaptation in the App
-```
+```dart
 class MyApp extends StatelessWidget {
 class MyApp extends StatelessWidget {
   @override
   @override
   Widget build(BuildContext context) {
   Widget build(BuildContext context) {
@@ -213,7 +213,7 @@ Column(
 #### Setting font does not change with system font size
 #### Setting font does not change with system font size
 
 
 APP global:
 APP global:
-```
+```dart
  MaterialApp(
  MaterialApp(
         debugShowCheckedModeBanner: false,
         debugShowCheckedModeBanner: false,
         title: 'Flutter_ScreenUtil',
         title: 'Flutter_ScreenUtil',