Set New React Application
Lets start without our root file public/index.html
load in three CDNs in the head - React, React DOM, and Babel.
React - the React top level API
React DOM - adds DOM-specific methods
The entry point for our app will be the root div element, which is named by convention.
Go ahead and delete all the files out of the /src directory, just keep index.css and index.js.
Just Copy the Bootstrap or whatever CSS framework you want, or nothing at all.
import React, ReactDOM, and the CSS file.
and render the App to the root as before at the last
This time, we're loading the Component as a property of React, so we no longer need to extend React.Component as class App extends React.Component