Nice, or as a tampermonkey user-script:

// ==UserScript==

// @name HN dark mode

// @namespace http://tampermonkey.net/

// @version 0.1

// @description HN dark mode

// @author You

// @match https://news.ycombinator.com/\\*

// @icon https://www.google.com /s2/favicons?sz=64&domain=ycombinator.com

// @grant none

// ==/UserScript==

(function() {

    'use strict';

    document.documentElement.style.filter = "invert()";

    document.documentElement.style.background = '#fff';

})();