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.

Nick Halsey

WordPress core provides custom CSS functionality in the customizer that’s specific to the current theme; you can switch themes freely with each theme’s additional CSS remaining in place. Sometimes, you need some CSS to apply regardless of the current theme persistently. This plugin adds a plugin CSS option for CSS that’s global and persists across theme changes.
With the Customizer, your CSS is instantly live-previewed, offering the ability to see exactly how your site will look before you publish your changes. The plugin CSS option is stored as an <code>option</code>. Prior to WordPress 4.7 (which introduced additional CSS in core), theme-specific CSS was stored as a <code>theme_mod</code>, in 4.7 and newer this is migrated to the core CSS functionality (which is theme-specific).

Modular Custom CSS

WordPress core provides custom CSS functionality in the customizer that's specific to the current theme; you can switch themes freely with each t …

Legacy Jetpack Custom CSS Editor vs Modular Custom CSS