A 24-year-old female computer programmer presents with an asymptomatic, non-blanching reticular discoloration on her anterior thighs that has progressed over 6 months. She works 8–10 hours daily with her laptop resting on her lap. On examination, the pattern marked **A** in the diagram shows a reddish-brown, net-like reticulated appearance with fine telangiectasias and slight scaling, sparing adjacent uncovered skin. There is no pain, pruritus, or systemic symptoms. Which of the following is the most likely diagnosis and primary causative mechanism?