Implement a dark mode (and a toggle)

[retailcoder]

The site is vanilla Bootstrap with very little customization - there is a bit of CSS around syntax highlighting that is intended to look like the VBE, so it would be interesting to limit the palette to the 16 available in the VBE (perhaps the blue background? IDK the palette is very harsh, maybe play around it)

[Voidless7125]

I will start working on it tomorrow.