I looked at your example and did the following to my book.
Created a new stylesheet, left the name and entries Sigil gave, copied the CSS from the old to the new file, and updated with this line in the file <head>
Code:
<link href="../Styles/Style0001.css" rel="stylesheet" type="text/css"/>
That is the only difference I can find between the two books. I had stylesheet.css in the root so I could link directly. Guess Sigil didn't like that?
I was using the Sigil built-viewer and Calibre Book Viewer. I hadn't yet copied to Moon Reader on the phone, did that now, and the fonts are showing.
Thank you both Kevin and Becky