update to React 18

src/index.js

@@ -1,15 +1,17 @@
 import React from 'react';
-import ReactDOM from 'react-dom';
+import { createRoot } from 'react-dom/client';
 import App from './App';
 import reportWebVitals from './reportWebVitals';
 import './responsive.js'
 
-ReactDOM.render(
+const container = document.getElementById('root');
+const root = createRoot(container);
+root.render(
   <React.StrictMode>
     <App />
-  </React.StrictMode>,
-  document.getElementById('root')
-);
+  </React.StrictMode>
+  );
+
 
 // If you want to start measuring performance in your app, pass a function
 // to log results (for example: reportWebVitals(console.log))