Mui Button not working: Uncaught Error: Invalid hook call. Hooks can only be called inside of the body of a function component

Question

->> SOLVED: npm install @mui/material @emotion/react @emotion/styled

I just copied this from the mui site and installed it via npm install @mui/material.
This is my index.js file:

import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import Button from '@mui/material/Button';

ReactDOM.render(
  <React.StrictMode>
    <Button variant="contained">Hello World</Button>;
  </React.StrictMode>,
  document.getElementById('root')
);

I get this error: Uncaught Error: Invalid hook call. Hooks can only be called inside of the body of a function component.