Hi dennybop ,
@Neus was talking about WordPress' built in CSS inserter.
To add the custom CSS on your site, go to your WordPress dashboard.
From there, go to Appearance -> Customize -> Additional CSS .
You can then paste the code above in there. 😁
Here's a video guide on how to find this:
How to Easily Add Custom CSS to Your WordPress Site
The name might change on some custom theme but it it should be around the same.
Let me know if you are able to insert the custom CSS! 😃