why do i get this message in the console when i refresh ``The development server has disconnected. Refresh the page if necessary``

Created by: Johnnycapreano

i was reading from a book on react all i did is use the command create-react-app to followed by the app name to create the app i used the command yarn start to run my app i added this code to my app.js file `` <div className="Example" style={{ background: "white", color: "white" }} onClick={() => alert('hello')}>

`` when i run i get redirected to page on localhost 3000 i have white screen all in my console is this message`` [HMR] Waiting for update signal from WDS... `` when i refresh to see the changes i made to app.js file i get this message in the console``` The development server has disconnected. Refresh the page if necessary.``` and still nothing on the screen how do i fix that