We need to edit the site in design mode.
Select any page and click on the ‘>’ icon. You will see the settings page.
Scroll to the end of the settings and you will find the custom code.
To add script or css to the entire website visit the url https://webflow.com/dashboard/sites/xxxxx/code – replace xxxxx with your site code.
You will find the Custom Code window. You can specifically add code to head/footer.