A CSS library is composed of the URL of an external StyleSheet resource and/or a custom CSS code that is automatically added in the head of the template.
Implement an CSS library by attaching it to a default template from the back-end.
1 – To add new StyleSheet from back-end click on Live Editor > Web Resources
2 – You can now add a new CSS library or edit an existing one.
4 – Add a CSS URL and StyleSheet to a CSS library inside the content field.