Basemaps are the foundation for your layers and while there are plenty to choose from in the default basemap gallery and others to choose from Living Atlas, you can also create your own. Two blogs from Andy Skinner, cartographic designer on the Living Atlas team, explain how.
Build your own sandwich shows how you can use the Vector Tile Style Editor (VTSE) to start with an existing vector tile basemap and customize it.
Map Bases: Mixing it up also covers VTSE, but adds blending and another option to achieve your desired result.
Once you've created your custom basemap, here's how to add them to a custom basemap gallery for your organization.