total darkness; utter darkness
A literary yojijukugo meaning pitch-black darkness, as dark as a moonless night. Rare in modern conversation; mostly encountered in classical or poetic contexts.
Inside the cave it was pitch-dark, and I couldn't see a step ahead.
Common everyday word for total darkness. 如法暗夜 is a rare, literary yojijukugo with a more classical feel.
General word for darkness. 如法暗夜 emphasizes an extreme, utter darkness, often in a literary or dramatic context.
如法 is used adverbially here in the sense “thoroughly” or “utterly,” modifying 暗夜 “dark night.” The compound therefore denotes complete darkness.