Answer 1

Remove form element,then the screen doesn't disappear,you are not be able to make after login,becoz you don't know how to add cdn of jQuery .
see your own code.
https://code.sololearn.com/WFLA6NyO1GIc/?ref=app

and see my code
https://code.sololearn.com/W4YD8LB6ovQm/?ref=app

Answer 2

🎃#H P 22™🎃 You are getting a white screen because in a actual website when we fill a form and tap the submit button ,all the form data is sent to server using method, get or post but here you are not working on an actual website so you can replace the type attribute of the login button from "submit" to "button".
<input type="button"/> and white screen will not appear!