Design a luxurious penthouse interior with a sophisticated blend of black and white marble, complemented by brushed steel accents. Use striking black marble for the flooring or key wall features to create a dramatic, elegant base. Incorporate white marble for countertops, fireplace surrounds, or statement walls to add a sleek, contrasting element. Incorporate brushed steel elements throughout the space--such as for light fixtures, furniture legs, and decorative accents--to provide a modern, industrial touch. The furniture should be high-end and minimalist, with clean lines to complement the marble and steel materials. Add plush, neutral-toned textiles like gray or cream to balance the boldness of the marble and steel. Use warm, layered lighting to highlight the textures of the marble and steel, creating a cozy yet refined atmosphere. Include large windows or glass doors to maximize natural light and showcase panoramic views. Finish the look with carefully chosen art pieces and decorative accessories in metallic finishes to tie the sophisticated design together.