Apply suggestion from @afc163

src/components/RightContent/index.tsx

@@ -1,6 +1,8 @@
 import { QuestionCircleOutlined } from '@ant-design/icons';
 import { SelectLang as UmiSelectLang } from '@umijs/max';
 
+import React from 'react';
+
 export type SiderTheme = 'light' | 'dark';
 
 export const SelectLang = () => {