Create an ultra-premium jewelry advertising poster for a fictional brand "CÉLESTE". FORMAT: 4:5 vertical, elegant editorial layout. SUBJECT: a single diamond necklace draped over a smooth black marble curve, brilliant facets catching sharp sparkles of light. BACKGROUND: deep obsidian-to-charcoal gradient with soft golden glow, subtle floating light particles. LIGHTING: precise jeweler's spotlight creating crisp diamond sparkle, luxurious deep shadows. TYPOGRAPHY: refined thin serif brand name "CÉLESTE" centered top, tiny tagline "Light, eternal" at the bottom, generous negative space. FINISH: 8k, hyper-realistic, opulent high-end commercial finish.