Design and iterate end-to-end UX for a B2B marketplace to improve add-to-cart, first/second purchase conversion, and feature adoption across web and mobile. Produce wireframes, prototypes, user flows, and high-fidelity specs; maintain component library/style guide and information architecture. Partner with Product and Engineering, use analytics and user research to identify opportunities, lead design reviews, and ensure implementation fidelity through handoff and QA.