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.

Adnan

WPBrigade

Muhammad Irfan

WP Headers and Footers plugin helps you to insert code to your WordPress website headers and footers section like Google Analytics tracking code, Facebook Pixels code, Google Optimize code for A/B testing, Custom CSS code, and more. You don’t need to edit the theme files to insert the code.
The simple interface of this plugin allows you to add code and different scripts from one place to your WordPress website (Headers, Footers, and Body section).
Features
<ul>
<li>Insert code to your WordPress headers & Footers</li>
<li>Insert Google Analytics Code to any WordPress theme</li>
<li>Insert Facebook Pixels Code</li>
<li>Add Google Optimize Code for A/B testing ( Ab Testing )</li>
<li>Add Google search console authentication code to any theme for verification</li>
<li>Add Custom CSS, any script, and HTML to your website 
Google Tag Manager code/script insertion</li>
<li>You can also insert code to your website body section 
Can add Bing webmaster tool code for website verification 
Add Google AdSense code</li>
</ul>
If you find our plugin useful, please leave a good rating/review and check our other plugins.
<ul>
<li><a href="https://analytify.io/ref/73/?utm_source=wp-headers-and-footers&utm_medium=readme&utm_campaign=pro-upgrade" rel="nofollow ugc">Analytify – Google Analytics Plugin</a></li>
<li><a href="https://loginpress.pro/" rel="nofollow ugc">LoginPress</a> – For Custom login page and login page security</li>
<li><a href="https://simplesocialbuttons.com?utm_source=wp-headers-and-footers&utm_medium=readme&utm_campaign=pro-upgrade" rel="nofollow ugc">Simple Social Buttons</a> – Plugin for Social share buttons and social icons</li>
<li><a href="https://wordpress.org/plugins/related-posts-thumbnails/">Related Posts Thumbnails Plugin</a> – For related posts/products</li>
<li><a href="http://wpbrigade.com/recommend/maintenance-mode?utm_source=wp-headers-and-footers&utm_medium=readme&utm_campaign=pro-upgrade" rel="nofollow ugc">Under Construction, Coming Soon & Maintenance Mode</a> – Plugin for Under construction & Coming soon page</li>
</ul>

Insert Headers And Footers

I like its simple design which doesn't add menu item on top level of WP admin menu. Recommended for client works and who prefer to keep WP admin menu simple. I hope you continue its simple style than adding functionalities.

Simple UI

Include inline javascript, stylesheets, CSS code or anything you want in Header and Footer areas of your WordPress with ease.

Legacy Jetpack Custom CSS Editor vs Insert Headers And Footers