NimbusOS Footer — Référence de design web et prompt

# Prompt: NimbusOS footer section

Build a single-file **footer section** for a fictional digital-growth agency, **NimbusOS**. Use plain HTML, CSS and vanilla JS, with no framework and no build step. A deep indigo, photographic "sky" with a soft diagonal light fold fills the screen. A white newsletter call-to-action sits on it at the top left, and a crisp white footer card floats above a striped indigo floor at the bottom.