♻️ refactor(App): make explicit root element

src/main.tsx

@@ -7,7 +7,8 @@ import App from './App.tsx'
 import theme from 'style/theme.ts'
 import './index.css'
 
-ReactDOM.createRoot(document.getElementById('root')!).render(
+const root = ReactDOM.createRoot(document.getElementById('root') as HTMLElement)
+root.render(
   <React.StrictMode>
     <ThemeProvider theme={theme}>
       <CssBaseline />