Sorry, code is not public. My initial business model was to offer the shade layer as a drop in for any Leaflet, Mapbox, Google Map so companies like AllTrails, Strava, Gaia GPS could use it in their apps but selling's hard. Now I'm leaning a bit towards just releasing an app with offline mode.
Great link, thanks. Horizontal scrollbar tripped me out a little bit though...
It also takes into account the Earth's curvature, so you can zoom out to planet level and it still works.