For HTML Day 2025 [1], I made a web service that displays the current sky at your approximate location as a CSS gradient. Colours are simulated on-demand using atmospheric absorption and scattering coefficients. Updates every minute, without the use of client-side JavaScript.
Source code and additional information is available on GitHub: https://github.com/dnlzro/horizon
[1] https://html.energy/html-day/2025/index.html