Dark-mode

[rpede]

I found an issue with this document.

Title: Fly.io developer documentation
Location: https://fly.io/docs/
Source: https://github.com/superfly/docs/blob/main/index.html.md

Describe the issue

No obvious way to switch documentation pages into dark-mode.
This issue can cause significant eye strain when working in a dimly lit environment.

Expected behavior: automatic switch between dark/light-mode depending on system settings.
See prefers-color-scheme.

Optional: provide a toggle to manually change between light and dark theme.