Fonts lost on Kindle

I'm new to this.

I have set up my epub fonts in CSS. All looks fine in Kindle Previewer.

I presumed I should use an online converter to get azw3 format for the Kindle app. So I converted the epub.

When I open the azw3 in Kindle for Mac, my fonts are gone. Previewer said "Publisher's Font' when I viewed it there. But there is no selection in Kindle for Mac.

Help, please. I am obviously missing something.

THX