Only use code you are familiar with and from a source that you trust.
It is a good idea to use the Site Backup Feature before adding custom code.
This feature gives you access to the <head> HTML section, <body end> HTML section, and allows you to configure quick navigation. For access to other HTML Predefined Sections see Developer Mode.
We cannot assist in troubleshooting custom code.
Access the Header HTML Section
In the left panel, click Settings.
Click Head HTML.
AJAX Page Changing (Quick Navigation). Click the Enable AJAX Page Changing toggle to replace the body content of the current page without changing the head for faster navigation.
Head HTML. Add content to the head section field.