How to get the CSS-Selector of a disappearing message

I am trying to get the CSS Selector of the error message being displayed in the login/signup screen in https://automationexercise.com/login

I tried the solution given in How to find the element of a toast message in chrome but message still disappeared after the site was paused/frozen. I also tried to find it using the ctrl f in the Elements tab of the DevTools, is there a way to get the CSS Selector for this object?

These messages appear every time you enter a non-email into an input with type="email" and submit the form. It's not an element at all.