This plugin will allow you to add custom CSS only for chosen pages or posts and also for your entire website. No matter how often you’ll update the theme, your work will not be overwritten by the theme update.
Demo https://codecanyon.net/item/infinito-custom-css-for-chosen-pages-and-posts-or-for-entire-website-wordpress-plugin/22908708
Downloadhttps://www.filecad.com/mqLS/INFINITO-v1.0---Custom-CSS-for-Chosen-Pages-and-Posts.rar