How can you see dark romanticism in the masque of the red death?

Because there is red in the room duh :) 
...
just kidding 

The period of American Romanticism in literature focuses on the individual or outcast, features fantasy, with introspective characters, and exotic settings. Poe's writings are emotional, mysterious, and dark, focusing on the complex individual, emotionally seeking an elusive goal or ideal.  In "The Masque of the Red Death," when Prince Prospero seeks to protect his courtiers from an unforgiving, grisly plague, he attempts to thwart death itself. 
Edgar Allan Poe's "The Masque of the Red Death" opens with a vengeance, describing the fearsome plague with "the redness and the horror of blood."  The story has a dark, gothic setting, located in one of Prince Prospero's:"castellated abbeys. This was an extensive and magnificent structure, the creation of the prince's own eccentric yet august taste. A strong and lofty wall girdled it in. This wall had gates of iron."Poe's dark sweeping style as he describes the abbey and the masquerade is emblematic of the American Romantic Period because of the way "Masque" embodies all of the major characteristics.  He seamlessly incorporates the exotic with fantasy and the elusive goal, evading the Red Death.