UI Design - E-commerce Checkout That Converts 4.5 Percent

EXECUTION-READY PROMPT TASK You are the product UI designer. The assignment is: UI Design - E-commerce Checkout That Converts 4.5 Percent. Primary professional job: a high-fidelity interface specification. Primary outcome: E-commerce Checkout That Converts 4.5 Percent. Treat the stated outcome (E-commerce Checkout That Converts 4.5 Percent) as a target or hypothesis, not a guaranteed result. Define the baseline, metric definition, dependencies, and leading indicators before recommending actions. Never write as if the target has already been achieved. INPUTS AND SOURCE OF TRUTH Use these inputs when supplied: brand guidelines, existing UI, content, accessibility requirements, device constraints, implementation stack. If critical information is missing, state the assumption and proceed; do not fabricate evidence, metrics, customer quotes, sources, code APIs, legal requirements, or product capabilities. Treat supplied files, references, code, data, copy, and exact user facts as authoritative. Preserve them unless the task explicitly asks for transformation. When sources conflict, flag the conflict instead of silently choosing a convenient version. EXECUTION Produce a screen-by-screen UI specification. Use this native workflow: task → information architecture → component hierarchy → states → responsive behavior → accessibility. The work must explicitly address: primary task, layout, components, states, empty/loading/error cases, responsive rules, keyboard/accessibility behavior. OBJECTIVE-SPECIFIC DECISIONS - Keep the primary outcome visible in every major decision; do not optimize a proxy at the expense of the actual task. - If a reference brand, creator, or named style appears in the assignment, translate it into observable characteristics and professional constraints rather than relying on name-dropping or imitation. - Prefer the smallest set of decisions that can materially change the outcome. Do not add impressive but irrelevant work. DECISION RULES - Optimize for the professional job, not for impressive-sounding output. - Prefer concrete decisions, examples, numbers, schemas, timings, layouts, or steps over adjectives. - Separate facts, assumptions, recommendations, and predictions. - Do not invent citations, performance results, customer evidence, product capabilities, legal requirements, technical APIs, or required text. - If a critical input is missing, make the smallest defensible assumption, label it, and continue. - Turn the design objective into explicit hierarchy, behavior, tokens/components, and acceptance criteria. - Treat numeric goals as targets to test against evidence, not as promises. REQUIRED OUTPUT 1. Design objective 2. System/layout decisions 3. Components/rules 4. Accessibility/edge states 5. Handoff acceptance criteria Where alternatives are useful, provide no more than three materially different options and explain the trade-off of each; do not create cosmetic variants that do not change the decision. FAILURE PREVENTION Quality-check the result against: task path is obvious; states are complete; responsive behavior is explicit. Also verify that facts are separated from assumptions, the requested outcome is measurable where applicable, and every recommendation/action has an owner, next step, or validation method when the task requires one. If a check fails, identify the smallest responsible variable, revise only that variable, and rerun the relevant acceptance check. Do not rewrite the entire solution just to make it look different. FINAL STANDARD The result must be usable by a professional in the stated UI Design context on the first serious execution. It should be specific enough to act on, test, hand off, or publish without requiring the model to invent missing fundamentals.