Joe Dolson

Adds a custom field to your post editing screens to add custom styles applied only on that page or post.
Attach custom styles to any page, post, or custom post type. Separate styles can be attached for print, screen, or mobile. You can also store your own library of frequently-used styles.
How to use the style library:
<ol>
<li>Add the styles you want on your settings page.</li>
<li>Navigate to an article which requires specific styles.</li>
<li>Select the library style from the drop down, leaving the style textarea blank.</li>
<li>Update or post the new document.</li>
</ol>
A newly-selected style from the style library will always overwrite any previous hand-written styles. If you wish to alter the library styles for a specific page, you can do this in the textarea after you’ve saved the page with the style library template.
By default, editing your saved stylesheets will have no impact on previously saved post-specific styles; set the option to pull styles from the library to change this.
Note: custom styles will not be included on archive pages; only on single post/Page views.
The use you’ll get out of this plugin depends on the flexibility of the theme you’re using and your own knowledge of CSS (Cascading Style Sheets).

WP Post Styling

Define custom styles for any post, page, or custom post type. Example: journal-style publications which want to create a unique design for articles.

John Regan

Add Custom CSS to your WordPress site without any hassles.
An easy-to-use WordPress Plugin to add custom CSS styles that override Plugin and Theme default styles. This plugin is designed to meet the needs of administrators who would like to add their own CSS to their WordPress website. Styles created with this plugin will render even if the theme is changed.
New in Version 4.0.7
<ul>
<li>Tested for compatibility with WP 6.7.2</li>
<li>Tested for compatibility with PHP 8.4</li>
</ul>
<h3>Features</h3>
<ul>
<li>AMP Support</li>
<li>Customizer Control (live preview)</li>
<li>Useful Code Syntax Highlighter</li>
<li>Code linting (error checking)</li>
<li>No configuration needed</li>
<li>Simple interface built on native WordPress UI</li>
<li>Virtually no impact on site performance</li>
<li>No complicated database queries</li>
<li>Thorough documentation</li>
<li>Allows Administrator access on WP Networks (Multisite)</li>
</ul>
<h3>Usage</h3>
<ol>
<li>
Navigate to Appearance > Custom CSS in the Admin Menu
</li>
<li>
Enter in valid CSS styles
</li>
<li>
Click “Update Custom CSS”
</li>
<li>
View your changes in the Front End of your website
</li>
</ol>
<h3>Help</h3>
<a href="https://github.com/johnregan3/simple-custom-css/wiki" title="Simple Custom CSS Wiki" rel="nofollow ugc">Simple Custom CSS Wiki</a>
<a href="https://wordpress.org/support/plugin/simple-custom-css" title="Support Forum" rel="ugc">Support Forum</a>

Simple Custom CSS Plugin

This is one of the best Custom CSS Plugin I've ever used. I've been using it since 2016. This plugin works very well.

Simple but works really good.

Add Custom CSS to your WordPress site without any hassles.

WP Post Styling vs Simple Custom CSS Plugin