Create one standalone premium abstract textured background image for web design. No text, no letters, no interface, no logos, no watermark, no border, no collage. Full bleed. Tactile irregular stochastic grain integrated into the colors, not a visible repeating pattern. Keep useful quiet negative space for website copy. Ultrawide 21:9. Three broad shallow sweeping curved bands in midnight teal, ocean blue and icy pale cyan crossing the lower third from edge to edge. Medium irregular photographic grain, softly airbrushed boundary transitions, restrained luminous color. Upper two thirds almost-black deep teal negative space for centered text. Flat abstract graphic landscape, not actual waves, no scenery, no purple.