diff --git a/README.md b/README.md
index 5af61f7..e36c196 100644
--- a/README.md
+++ b/README.md
@@ -1,28 +1,35 @@
-# overlay_support 
+# overlay_support
+
 [![Pub](https://img.shields.io/pub/v/overlay_support.svg)](https://pub.dev/packages/overlay_support)
 [![Pub](https://img.shields.io/pub/v/overlay_support.svg?include_prereleases)](https://pub.dev/packages/overlay_support)
 [![CI](https://github.com/boyan01/overlay_support/workflows/CI/badge.svg)](https://github.com/boyan01/overlay_support/actions)
 [![codecov](https://codecov.io/gh/boyan01/overlay_support/branch/master/graph/badge.svg)](https://codecov.io/gh/boyan01/overlay_support)
 
-
 Provider support for `overlay`, make it easy to build **toast** and **In-App notification**.
 
 **this library support ALL platform**
 
 ## Interaction
 
-If you want to see the ui effect of this library, just click here [https://boyan01.github.io/overlay_support/#/](https://boyan01.github.io/overlay_support/#/)
+If you want to see the ui effect of this library, just click
+here [https://boyan01.github.io/overlay_support/#/](https://boyan01.github.io/overlay_support/#/)
 
 ## How To Use
 
 1. add dependencies into you project `pubspec.yaml` file
-```
-dependencies:
-  overlay_support: latest_version
-```
-  * Current latest_version is [![Pub](https://img.shields.io/pub/v/overlay_support.svg)](https://pub.dev/packages/overlay_support)
+
+    ```yaml
+    dependencies:
+        overlay_support: latest_version
+    ```
+
+    * Current latest_version
+      is [![Pub](https://img.shields.io/pub/v/overlay_support.svg)](https://pub.dev/packages/overlay_support)
+
+> For project without migrate to null safety, please use version `overlay_support: 1.0.5-hotfix1`
 
 2. wrap your AppWidget with `OverlaySupport`
+
 ```dart #build()
   return OverlaySupport(child: MaterialApp());
 ```
@@ -33,24 +40,23 @@ dependencies:
 import 'package:overlay_support/overlay_support.dart';
 
 void onClick() {
-  // popup a toast.
-  toast('Hello world!');
+    // popup a toast.
+    toast('Hello world!');
 
-  // show a notification at top of screen.
-  showSimpleNotification(
-    Text("this is a message from simple notification"),
-    background: Colors.green);
+    // show a notification at top of screen.
+    showSimpleNotification(
+        Text("this is a message from simple notification"),
+        background: Colors.green);
 }
 ```
 
 more instructions check here :  [example/README.md](./example/README.md)
 
-## License 
+## License
 
 see License File
 
 ## End
 
-if you have some suggestion or advice, please open an issue to let me known. 
-This will greatly help the improvement of the usability of this project.
-Thanks.
+if you have some suggestion or advice, please open an issue to let me known. This will greatly help
+the improvement of the usability of this project. Thanks.