This pattern is used for referencing custom CSS files.
How this works
Include custom CSS
Yes - Indicates that custom CSS will be used.
Selecting this option causes the CSS reference group to be displayed.
No - Indicates that custom CSS will not be used.
CSS reference
This group contains all the fields necessary for defining a reference to a single CSS file.
You can define multiple CSS references by using the Add new group 
button to the right of the group label.
Type
Asset - Indicates the CSS file is located in Cascade as a part of your site.
Selecting this option causes the File field to display.
URL - Indicates the CSS file exists somewhere on the web.
Selecting this option causes the URL, Crossorigin handling, and Integrity fields to display.
File
Only displayed when Type is set to ‘Asset’.
Use the asset chooser to select the desired CSS file in your Cascade site.
URL, Crossorigin handling, and Integrity
Only displayed when Type is set to ‘URL’.
Enter the full URL of the CSS file in the URL text field. Some websites also provide integrity and crossorigin attribute values with their hosted files.
<link .... crossorgin=”....” integrity=”....” />
Use the Crossorigin handling and Integrity fields to provide the respective values.