Scrolling tab not working

Can someone explain why the vertical scrollbar doesn’t appear in this notebook? (if this is the right place to ask)

jupyter --version 4.4.0 jupyter notebook --version

I realized that I failed to mention the browser: OSX Chrome Version 73.0.3683.86
And I’ve since learned that this problem - a vertical scrollbar not appearing in a tab widget, does not happen on other OS/browser combinations. E.g., it works fine on an earlier version of Chrome on Windows, works on Windows/Edge, works on OSX/Safari.

I don’t suppose there’s a testing dashboard of Jupyter issues on various browsers?