Add a docs section on TailwindCSS, cn(), how dark mode works, fonts, etc

[vincanger]

A general section on what's going on under the hood with regards to Tailwind and styles could be beneficial to users.

[Lansa-18]

@vincanger Good day.
Can I get this assigned to me?

[vivekfyi]

Hi @vincanger , can you please assign this to me.

Thanks.