Swap the warning box for a pop up

[AnthonyLim23]

@wilkojohnny do you have a preference for what sort of pop up (see https://www.dash-bootstrap-components.com/docs/components/modal/)?

Happy for you to decide, but i like the 'Vertically centered modal' one. The only one I disliked was the one that doesn't let you press 'Esc'!

[wilkojohnny]

I agree -- happy with the vertically centred one, and I also can't stand the one where you can't press Esc :)