How can I define a stylesheet for customer widget

I successfully created a customer widget as described in How To - Create A Custom Widget (WebIQ >= 2.13).

Now I want to assign a style sheet to the customer widget, but my customer widget is not displayed in "Code Manager" "Stylesheets" template list.

1. How can the customer widget added to the template list of the stylesheets
2. How can I define the template content which is used when the stylesheet of my customer widget is created?