A 2-month-old infant is brought to the clinic for evaluation of a birthmark on the face that has been present since birth. The lesion is a flat, well-demarcated, blanchable erythematous patch involving the right forehead and upper eyelid. It respects the midline and has not changed in size or color since birth. The infant’s parents ask whether the lesion will go away on its own. Which of the following is the most likely diagnosis?