google-dark.user.css

/* ==UserStyle==
@name         Google Dark
@description  Dark theme for Google
@namespace    pblew.dark-themes
@version      1.0.3
@author       Paul Blew <paul.blew@gmail.com> (https://github.com/pblew/dark-themes)
@homepageURL  https://github.com/pblew/dark-themes
@supportURL   https://github.com/pblew/dark-themes/issues
@license      CC-BY-4.0
@preprocessor default
==/UserStyle== */

@-moz-document regexp("^https?://www\\.google\\.co(?:m|\\.[a-z]+)/.*$") {
    html:not([stylus-iframe]) > body {
        background-color: black;
        filter: invert(90%) hue-rotate(180deg);
    }
    div.gbip, img, span.gbii {
        filter: hue-rotate(180deg) invert(90%);
    }

}