From the active cable chatroom series how to I fix the size of the chatroom and scroll

I have implemented the chatroom but I want the chatroom area to be fixed and for the user to be able to scroll back through the messages.
How can I add scrolling? I have tried added it to the panel the contains the chat but it is ignored? Any ideas?

I know Slack uses flexbox to do their layout. Something like this codepen: http://codepen.io/tutsplus/pen/XJexGg

Scrolling should be automatic if you have enough messages in the view. You can also force the scroll bar by adding overflow-y: scroll.