Are you looking for the solution for applying the page level CSS instead of putting it in customization->add additional CSS tab which generally applied to all the pages and sometimes that it hurts the whole website and break the complete layout of the website, because when you put the CSS in the customization -> add additional CSS tab, the code is added to the global CSS file which is called throughout the theme, means you will note its effect on every page.
If you want to hide some boxes at the particular page or want to manage boxes height, want to apply colors and size on fonts. you strictly need a page-level CSS option which helps you in all these problems.
Most of the paid plugins have the option for page-level CSS below every page but for the free themes it’s not.
Here is a plugin that adds a particular box of custom CSS below every page, as you can add that page CSS easily.
Post/Page specific custom CSS:
Note: kindly note that “Post/Page specific custom CSS” plugin is written in PHP, write proper and valid CSS because every CSS you will write will be executed smoothly (back-end logic of the plugin ), writing wrong CSS will hurt your website.
I hope this short article will help you in achieving your small tasks, related to CSS.