For individual adjustments and to check changes immediately, the Customizer is a useful option. You won’t need a child theme and any update to the theme won’t delete your progress. However, if you choose to add a new theme, some or all of your changes may not be applied. The steps are as follows:
- Create a backup to prevent possible errors.
- Log in to the backend.
- Find the Customizer under “Design” in the left-hand menu.
- Scroll down and click “Additional CSS”.
- This launches an interface to enter your code into. With live preview, you can monitor in real time how changes made to the WordPress CSS will appear. The Customizer points out errors in the code.
- If you’re satisfied with your edits, save the changes, publish them or schedule them for publication.
Note that when using the Customizer, changes are applied to all subpages unless specific pages are selected.