Define custom cell types?

[leotrs]

Is there a way to define custom cell types? Right now there are code cells, markdown cells, and raw cells. Say I want a fourth type that is just like a markdown cell but always has a gray background (or any other arbitrary CSS setting). How to do this?

A search for nbextensions that do this did not yield any results, so I thought I'd ask here. Thanks!

[jasongrout]

The Jupyter notebook format does not allow for more cell types.

[leotrs]

I think I can modify the LaTeX extension for my purposes. Thank you!