I just ran the check for extra files.
books from Feedbooks showed up
they have this usage in the stylesheet
	Code:
	@import "page.css";
 So is the usage correct or the check wrong?
Note once I open the file in Sigil, I have to correct the entry to read:
	Code:
	@import "../Styles/page.css";
 .
Sigil 3.4 flags the file as 'unused' (IIRC Sigil does not check any of the contents of the Stylesheet(s) )