There are quite a few custom css plugins , however majority of them apply the custom css site wide. If you want to apply the css to a specific page, then one approach is to make edits to the theme functions.php file. However this approach is not recommended , as the changes will be lost if you change the theme.
In this tutorial I will share a simple technique to add custom css to a specific Page or Post in WordPress. The best part is that we don’t need to make any edits to the templates files or the functions.php file. We will achieve this without using any custom css plugin.