A bluish-gray dark background map style for light-colored data overlay -- uses the [Tangram] (https://github.com/tangrams) library. This is a slight variation of Mapzen/Patricio Gonzalez Vivo's [blueprint style] (https://github.com/patriciogonzalezvivo/tangram-sandbox/blob/gh-pages/styles/blueprint.md)
A screenshot with some sample overlay data:
