I wrote a simple Tampermonkey script:

(function() { 'use strict';

    // Background Color
    let el = document.querySelector("#hnmain")
    el.style.backgroundColor = "#1A1B16"
    el.style.color = "lightgrey"
    document.querySelector("body").style.backgroundColor = "#1A1B16"

    // Font Color
    document.querySelectorAll("a").forEach(one => { one.style.color = "lightgrey" })
    document.querySelectorAll(".c00").forEach(one => { one.style.color = "lightgrey" })

})();