update ToC section in sandbox.md

packages/app/resource/locales/en_US/sandbox.md

@@ -1,16 +1,13 @@
-<div class="card">
-  <div class="card-body">
+# :memo: Table of Contents
 
-# Table of Contents
+Add `ToC` after some `#` signs.
+`Table of Contents` or `Table-of-Contents` is also OK.
 
 ```
-@[toc]
+# ToC
 ```
 
-@[toc]
-
-  </div>
-</div>
+## ToC
 
 # :memo: Block Elements
 

packages/app/resource/locales/ja_JP/sandbox.md

@@ -1,16 +1,13 @@
-<div class="card">
-  <div class="card-body">
+# :memo: 目次
 
-# 目次
+いくつかの `#` 記号に続けて `ToC` という文字列を記述します。  
+`Table of Contents` または `Table-of-Contents` でも構いません。
 
 ```
-@[toc]
+# ToC
 ```
 
-@[toc]
-
-  </div>
-</div>
+## ToC
 
 # :memo: Block Elements
 

packages/app/resource/locales/zh_CN/sandbox.md

@@ -1,16 +1,13 @@
-<div class="card">
-  <div class="card-body">
+# :memo: Table of Contents
 
-# Table of Contents
+Add `ToC` after some `#` signs.
+`Table of Contents` or `Table-of-Contents` is also OK.
 
 ```
-@[toc]
+# ToC
 ```
 
-@[toc]
-
-  </div>
-</div>
+## ToC
 
 # :memo: Block Elements