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.

Łukasz Nowicki

Post/Page/Product-specific custom code allows you to add custom CSS styles to individual posts, pages, or WooCommerce products. It provides a dedicated area in the editor screen where you can write your CSS code. You can also choose whether the CSS should apply only to the single view or also to archive-type views.
A new meta box will appear below the content editor on the edit screen for posts, pages, and products. You can enter any custom CSS there and decide whether it loads only on the single view or also on archive pages like category listings or product grids.
<h3>Requirements</h3>
This plugin requires at least WordPress 5.0 (remember always to keep your WordPress installation up to date!) and PHP 7.4 on your server.

Post/Page Specific Custom Code

Great plugin!

A very useful plugin

Add custom CSS to posts, pages, or WooCommerce products, with optional archive support. Includes a dedicated editor box.

WP Post Styling vs Post/Page Specific Custom Code