You've asked about the dark romanticism of the poem "The Raven" by Edgar Allan Poe.

Poe wrote during the age of romanticism in the late 1700s to the middle 1800s. You might consider the historical context of the movement as a reaction against the classicism of the previous era, when the focus in literature, art, music, and the like tended to be upon the rational, the analytical, the orderly, the neatly categorized, the harmonious, the ideals of the Enlightenment.

When romanticism burst onto the scene, its authors, poets, composers, and visual artists rejected everything classicist and swung the proverbial pendulum the other direction. The new movement focused on imagination, emotions, the natural world, the individual, and things that were irrational, unexpected, unpredictable, bizarre, and even grotesque and nightmarish, the latter of which were the epitome of dark romanticism.

For instance, the entire atmosphere of the poem "The Raven" feels gothic, dark, melancholy, heavy with emotions: anticipation, uncertainty, fear, depression, terror, and grief. Poe's word choices and turns of phrase emphasize that dark romantic atmosphere: "dreary" in line 1, "bleak December" in line 7, "dying ember" and "ghost" in line 8.

That the poem is about a single narrator and his experiences--grieving for Lenore and what she meant to him, hearing the knock at the door, encountering the raven--is also part of romanticism (emphasis of the individual and his or her own personal experience as valid); it turns to dark romanticism with the nearly voyeuristic viewpoint the poem's reader has on the depths of the narrator's vulnerability. Further, the narrator's experience of the disruptive raven as, he both hopes and fears, the ghost of his beloved Lenore (stanza 5) is evidence of dark romanticism, which did not shy away from that which was horrific, ghoulish, haunting, even if only imaginary in the end.