Notebook 7 "classic" template #1220
Description
With Notebook 7 coming out soon, we should probably update the classic HTML template to use the new Notebook 7 CSS.
I created one some time ago for Voila https://github.com/martinRenou/voila-retro, but it also contains an nbconvert template that could probably just be copy pasted into here https://github.com/martinRenou/voila-retro/blob/master/share/jupyter/nbconvert/templates/retro/index.html.j2
Once nbconvert uses a Notebook 7 "classic" template, we will probably need to update the classic template we have here.