I was under the impression that the Progressive part of PWA meant Progressive Enhancement.

I have a PWA that creates html/css in the build process. If JS is enabled, it acts as an SPA. If JS is disabled, it's a simple static site. If ServiceWorker can be used, caches the html/css I built which both the SPA and static site versions can use. If no SW, then fallback to AppCache/LocalStorage/etc.

The hardest part was finding a CSS framework that doesn't use JS and still can do menus/etc nicely.

This is correct - I would define PWA as a superset of Progressive Enhancement.