As I prefer to browse dark websites when I'm coding, here is a collection of personal dark themes in UserCSS format, so that you can easily install and use them with an extension like Stylus.
I mainly used dark blue colors for background, a slightly grey text color (plain white has too much contrast, Inter as the body font and Cascadia Code as the monospace font if you have them installed.
Fonts stacks and some colors are easily customizable, using the UserCSS settings or directly the CSS variables.
Each theme is made available under the MIT license.
Also supports the Scripting Reference part of the website.
This theme is made for the main Unity documentation website.
This theme is made for Unity packages documentations generated by DocFX, like these : Input System, UI, Universal Render Pipeline...