我是 react.js 的新手。我一直在遵循how-to-do-simple-form-validation-in-reactjs 中的说明，我可以运行http://localhost:3000/
但是在添加引导程序后index.js，我收到了这个错误
Failed to compile ./src/index.js Module not found: Can't resolve 'bootstrap/dist/css/bootstrap-theme.css' in 'C:\react-form-validation-demo\src'
import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import 'bootstrap/dist/css/bootstrap.css';
import 'bootstrap/dist/css/bootstrap-theme.css';
import App from './App';
import registerServiceWorker from './registerServiceWorker';
ReactDOM.render(<App />, document.getElementById('root'));
registerServiceWorker();
如果我删除下面这两行，它会起作用：
import 'bootstrap/dist/css/bootstrap.css';
import 'bootstrap/dist/css/bootstrap-theme.css';