"Create a vibrant, flat design banner background for an alternative asset investment platform focused on art and collectible marketplaces. Use smooth, eye-catching gradients to add depth and modernity to the scene. Incorporate abstract, flat shapes and minimalistic elements like floating art pieces, rare collectibles, and upward-trending charts. The backdrop should feature a sleek, futuristic city skyline, softly illuminated with warm gradient tones, symbolizing growth and opportunity. The color palette should consist of soft, modern hues of gold, silver, and deep blue, with vibrant gradient accents highlighting key elements such as the art and financial symbols."