Okay, let's start setting up the basic structure and logo for your social media app, Beco.

This sets up:

1. An index.html file as the main entry point.
2. A style.css file with CSS variables for light and dark modes using your specified cold blue (#A0D2DB) and cold dark blue (#3A405A) colors. It includes basic styling and uses @media (prefers-color-scheme: dark) to detect the user's system preference.
3. A logo.svg file containing a simple text-based logo for "Beco" using a gradient of the specified colors.
4. The HTML file embeds the SVG logo directly.

You can see the basic structure and the logo now. The CSS automatically adapts to your system's light or dark mode preference.