Define film noir as a genre.What are its thematic and stylistic hallmarks? What character types occur repeatedly?

Noir often includes a private detective who is drawn into a web of crime and murder by a femme fatale figure, a liberated woman who uses her body and sexuality as leverage against weak men.The films are often are leftist films that indict capitalism, deal with twists of fate, and end with the sacrifice of the protagonist.They often capitalized on post-World War II pessimism and bridged gangster films and pulp-novel traditions.They contained night-as-night shooting, low-key lighting/high-contrast lighting, and off-kilter framings.