How to add Custom Scripts
To add custom scripts like FB Pixel, GA tracking code, etc navigate to Settings > Insert Headers & Footer.
How to add Custom CSS
There are two ways to add custom css code.
To add sitewide CSS go to Appearance > Customize and click on Additional CSS. Please don’t forget to reload a page/site after publishing the code.
On Page/Template CSS
Open Page Builder and navigate to Advance > Custom CSS. How to use the CSS and Selector option please follow this article https://elementor.com/help/how-to-use-selector-in-the-custom-css-tab/