update checkbox docs

examples/docs/en-US/checkbox.md

@@ -40,7 +40,7 @@ Checkbox can be used alone to switch between two states.
 ```
 :::
 
-## Disabled State
+### Disabled State
 
 Disabled state for checkbox.
 

examples/docs/zh-CN/checkbox.md

@@ -55,7 +55,7 @@
 ```
 :::
 
-## 禁用状态
+### 禁用状态
 
 多选框不可用状态。