docs: Update Menu demo sample

components/menu/demo/submenu-theme.md

@@ -7,11 +7,11 @@ title:
 
 ## zh-CN
 
-内建了两套主题 `light` 和 `dark`，默认 `light`。
+你可以通过 `theme` 属性来设置 SubMenu 的主题从而达到不同目录树下不同主题色的效果。该例子默认为根目录深色，子目录浅色效果。
 
 ## en-US
 
-The Sub-menu will inherit the theme of `Menu`, but you can override this at the `SubMenu` level via the `theme` prop.
+You can config SubMenu theme with `theme` prop to enable different theme color effect. This sample is dark for root and light for SubMenu.
 
 ```tsx
 import { Menu, Switch, MenuProps } from 'antd';