Which classic children's book series underwent a strategic 'dual cover' rebranding in the early 2000s that significantly expanded its audience to include adult readers?

The publishing industry has evolved sophisticated marketing strategies to help books stand out in an increasingly crowded marketplace. Publishers and authors carefully craft brand identities that resonate with target audiences while bookstores employ various retail tactics to maximize sales. This trivia question explores an innovative brand identity strategy that transformed a classic literary series and revolutionized its market position.

This is a live public trivia poll on AIPolls.Net. Vote and see real-time results.

Harry Potter (with 'adult' black covers featuring sophisticated artwork)
Percy Jackson (with alternate 'mature reader' editions featuring Greek mythology-inspired designs)
Chronicles of Narnia (with minimalist covers targeting the fantasy literature community)
A Series of Unfortunate Events (with vintage gothic-styled covers for literary collectors)