Decadence is an interesting word. Literally it refers to something so old ;it is falling down. In literature the impression I have of it was a derogatory term for infatuation with antiquated and mildly grotesque immoral style, proposed by ultra-conservatist critcs. I think the Nazis used it against authors they hoped to stifle.
I expect some lumps for venturing that opinion.

Incidentally "Black Dahlia" was a hyped-up mysterious mourner who placed memorials of grave of Rudolph Valentino. Bet nobody remember him.
Dear WW: I doubt that there really is a black dahlia. It was so long ago, I don't remember why the mysterious lady was so called, most likely because she dressed in black.