Cartel promocional vertical

Design a vertical promotional poster for a retail campaign, laid out like finished marketing artwork rather than a photo. Build a clean background using a confident brand-forward color field or a soft two-tone gradient, and reserve a clear focal zone for the product or offer. Feature the described product or theme as the hero, rendered crisply with accurate color and material, and give it a subtle grounded shadow or a gentle glow so it sits convincingly on the layout. Establish a clear visual hierarchy: a dominant headline area at the top or center, a smaller supporting line beneath it, and a compact call-to-action element such as a rounded button or badge near the lower third. Render any text the user explicitly supplies exactly as written, spelled correctly, in a clean modern sans-serif with tight, legible kerning and strong contrast against the background; if the user gives no copy, leave tastefully composed placeholder blocks and shapes where text would go rather than inventing wording. Balance the composition with intentional negative space, aligned margins, and one clear accent color for emphasis. Keep it uncluttered, on-trend, and print-ready. Do not add fake pricing, invented brand names, watermarks, or messy stock-photo backgrounds. The result should look like a polished poster a design team would ship. User request: Summer sale, 30% off sneakers, headline "Step into summer"