Dark Mode for website

[shravanngoswamii]

Implementing Dark/Light mode in Quarto is straightforward, but I'm waiting because there isn't a 'cosmo' equivalent theme for Dark mode. It would require writing some custom CSS for 'solar' theme, which is similar to 'cosmo' but have some color inconsistencies that need refining.

@jitendravjh want to work on this - #80 (comment)

[jitendravjh]

Working on it, thanks for assigning me.