docs: dark mode, please 🙏🌚

[jamaluddinrumi]

it's common to had a dark mode version because it's reduce eye strain.
it's good for our health, so we can stay for coding in healthy eye.

[deadcoder0904]

@jamaluddinrumi use dark reader chrome extension in the meantime :)

[jamaluddinrumi]

i used that, but i like to open it in safari since in safari we had a less choices for dark mode extensions. btw, forget it, the docs is still convenient to read.