Hey there Coach, happy to see a fellow Ecosia user in the wild!
This map seems to be using Mapbox Streets for its’ style featuring vivid colors.
OSM has plenty of styles you can use. Here are some interesting ones that I found so far: www.mapbox.com/gallery/ openmaptiles.org/styles/
maps.stamen.com/#watercolor/12/37.7706/-122.3782
Toner is my favorite of these, as well as Dark Matter for mapping in the dark.
Though using them depends if they are integrated using Mapbox as we are relying on the configuration of the applet to provide these styles.