Create a premium vertical product advertising poster for a fictional premium tea brand "SERENE LEAF". Preserve bold modern product-poster logic: single hero teacup centered, fully saturated monochrome background, oversized headline behind the cup, vertical side label, short bottom descriptor. COMPOSITION: a delicate porcelain teacup filled with glowing amber tea slightly below center on a seamless soft sage-green background, a swirl of steam rising, dried tea leaves and a small flower suspended mid-air, one crisp diagonal shadow. TYPOGRAPHY: large bold cream stacked headline "CALM / RITUAL" behind the cup; slim vertical left label "ORGANIC WHITE TEA"; bottom line "HAND-PICKED, SUN-DRIED, TIMELESS." LIGHTING: strong clean directional light upper-left, glossy tea highlights, elegant shadow. STYLE: Cannes-level beverage advertising, luxury pop-minimal, ultra-real. NEGATIVE: cheap packaging, cluttered layout, plastic texture, muddy background, weak shadow, unreadable text, watermark. 8k.