A GL basemap style it is using the vector tile schema of OpenMapTiles as well as the contour lines and hillshading from maptiler.com.
Use the map editor in MapTiler Cloud to view and adjust this map. Open the editor and upload style from this repository or host from various styles available on the platform.
Or use the Maputnik CLI to edit and develop the style.
After you've started Maputnik open the editor on localhost:8000.
maputnik --watch --file style.json