cividi colors

[n0rdlicht]

Let's go all cividi and experiment a bit with dark mode options.

Reference for setting this up: https://squidfunk.github.io/mkdocs-material/setup/changing-the-colors/#custom-color-schemes

Colors we can start with:

• "cividi purple": #543076
• a cyan option (dark mode primary color?): #61BEBF
• standard mkdocs material whites, blacks, greys