The phrase "dark material" refers to something that is mysterious, unknown, or hidden. It often represents things that are difficult to understand or explain, and may cause feelings of uncertainty or fear. Full definition
When the impact occurred, darker material on the surface was blown away, and brighter material beneath it was revealed. (msss.com)
But the joking around doesn't so much complement the film's dark material as clash with it and undermine it. (rogerebert.com)
British writer Philip Pullman, creator of the His Dark Materials trilogy of children's books set in a dystopian alternative reality, described Trump as a «savage». (totalpolitics.com)