You're welcome, Antoine. I would strongly recommend though that you use Pro for this project because you won't need custom code to achieve this. You also would have lots of options if you use Pro. Since this is also not a feature offered in X and requires custom code to achieve, this essentially is theme modification and this is outside the scope of our support according to our Terms.
If you don't want to convert, I'd at least recommend that you use the Content CSS instead of the Global CSS. You can see the method in this similar guide at https://youtu.be/kre6O7AZKbM
The benefits of that are:
- The CSS @thai gave was page specific so it will be doing nothing for other pages so it will just add a bit of bloat globally.
- You won't have to do the page ID step.
Hope that adds more knowledge to you.