NNG Dark Mode

Stream: new members

[Utensil Song]

Also added night mode for anything on https://leanprover.github.io/ and https://leanprover-community.github.io/ locally, with just:

body {
    background-color: #202020 !important;
    filter: invert(1) hue-rotate(180deg);
}

using https://github.com/openstyles/stylus .

It looks like this:

image.png

The color can be tuned by changing the value before deg, and the color looks ok between 120deg and 180deg.

(Unfortunately, this (usually) universal dark mode style can't directly apply to NNG.)