So pardon my ignorance in all things GIS, but it looks like Mapy.cz serves the tiles which are based on OpenStreetMap. On that Mapy.cz site, there is no style that is similar to Windy. The maps I see are "Basic", "Traffic", "Outdoor", etc.

I'm interested in the grey/outlines basemap like this: https://www.windy.com/-Weather-radar-radar?radar,50.310,1.15... . The shading around the coastlines in particular is exquisite.

How did they generate this grey basemap? Does Mapy.cz offer the tools to generate such a map or do they just host the tiles?

Oh, I thought you meant the map which is visible if you zoom closer on Windy.

The gray map is probably custom made by Windy.

Actually that is an excellent map, thanks!