prompt: mobile app ui design for a university second-hand trading platform, homepage layout. top header with location and search bar. a banner for campus events. dual-column waterfall layout for product cards. the product cards have high-quality photos, price in vibrant orange, and tags showing "local pickup" and "verified student". bottom navigation bar with 5 icons. clean, minimal, youth style, campus blue and vibrant orange color palette, white background, light grey canvas. high resolution, dribbble style, ui/ux