How do you add Bootstrap Themes to REACT App.js

If by add "boostrap themes" you mean all the bootstrap CSS and styling, you can import it from the minified bootstrap package.

See getting started

Because React-Bootstrap doesn't depend on a very precise version of Bootstrap, we don't ship with any included CSS. However, some stylesheet is required to use these components.

CSS

{/* The following line can be included in your src/index.js or App.js file*/}

import 'bootstrap/dist/css/bootstrap.min.css';

Example:

import React from "react";
import 'bootstrap/dist/css/bootstrap.min.css';
import "./App.css";
import Nav from "./Nav";
import About from "./About";
import Shop from "./Shop";
import { BrowserRouter as Router, Routes, Route } from "react-router-dom";

function App() {
  return (
    <Router>
      <div className="App">
        <Nav />
        <Routes>
          <Route path="/about" element={<About />} />
          <Route path="/shop" element={<Shop />} />
        </Routes>
      </div>
    </Router>
  );
}