George Stephanis

This plugin re-adds a standalone editing page for Custom CSS 
in the WordPress Admin UI, for users that aren’t comfortable 
using the one in the Customizer.
Currently it only works with Jetpack and Jetpack’s added features, 
but shortly it will work without Jetpack as well, providing a 
more basic text editor without syntax highlighting.

Legacy Jetpack Custom CSS Editor

I was utterly dismayed to see the old Jetpack CSS editor disappear in favor of a little customizer box in WP 4.7. Thank you so much for restoring the legacy editor where we can actually see what we're working with, and where our designer can work with CSS without having to upload style.css every time they make a change. It's a vital part of our workflow and the little box in the customizer is completely inadequate.

many thanks for this lifesaver

This plugin re-adds the full page admin Custom CSS editor to Jetpack.

Benjamin Chris

WP Editor.md is a beautiful and practical Markdown document editor.
Build support for the WordPress using Editor.md.
The plugin uses the Markdown module from WordPress <a href="http://jetpack.me" rel="nofollow ugc">Jetpack</a> for parsing and saving content.Thank for Jetpack modules.

Legacy Jetpack Custom CSS Editor vs WP Editor.md – The Perfect WordPress Markdown Editor