Dark mode

[jkokocha]

Create a dark mode switch for the website. This switch should apply to all websites simultaneously and preferably be easily available. This switch should be in the header (navbar) and be accessible from all pages on the website.

This feature might require one to redo the colors used in certain pages, since some pages are light and some pages are dark at the moment of writing this.

If you create a dark mode feature that doesn't apply to all pages, it might still be accepted as a solution to this issue if there's a good reason for it.