First message scrolls out of sight on mobile if URL bar is open

[TimDuschenes]

First message scrolls out of sight on mobile.

I think this is being caused the interaction of two things:

1. vh ignores whether the URL bar of the browser is minimized or not, so the page is too tall if the bar is open
2. After each message is sent, the main section scrolls all the way to the bottom so you can see the new message

Is there a way to prevent this happening?
To see the issue in action, visit https://timduschenes.com/ChatBotv2.html on mobile