PHPFusion core have three custom include options and themes have one custom include option.
Create and paste any custom content under /includes with the following names:
For themes, you can replace the default Bootstrap CSS with a custom Bootstrap CSS file. Place your custom Bootstrap file in your /theme/custom_bootstrap/custom_bootstrap.css or custom_bootstrap.min.css.
Important: The file need to be named custom_bootstrap.css or custom_bootstrap.min.css