No puedo completar esa fase de configuración:
4. Add custom CSS
With that cleanup out of the way, you’re ready to add your custom CSS code.
This is the basic code you will use; In the following sections, we’ll guide you through customization to suit your needs:
If you’re using Elementor 2.9 and above, you can add this CSS via the global style rules:
Click on the hamburger menu icon at the top left corner of the Elementor interface
Choose Theme Style in the Global Style section
Select Custom CSS (once the theme styling interface has been opened, it will be blue instead of the “normal” red Elementor element)
Add the CSS code
Do you mean you want to add custom css to your website?
We have many ways to add these custom css to the website:
1. Add CSS and style.css file (child-theme)
2. Add Custom CSS to Customize CSS
3. Add custom CSS to Elementor custom css as you say, follow guide at https://elementor.com/help/global-custom-css/