Darken a page in Conkeror

A snippet to darken the current page you’re looking at (I ripped off a Greasemonkey script):

  
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function darken_page (I) {
    var newSS, styles='* { background: black ! important; color: grey !important }'
        + ':link, :link * { color: #4986dd !important }'
        + ':visited, :visited * { color: #d75047 !important }';

    var document = I.window.buffers.current.document;

    if (document.createStyleSheet) {
        document.createStyleSheet("javascript:'" + styles + "'");
    }
    else {
        newSS=document.createElement('link');
        newSS.rel='stylesheet';
        newSS.href='data:text/css,'+escape(styles);
        document.getElementsByTagName("head")[0].appendChild(newSS);
    }
}

interactive("darken-page", "Darken the page in an attempt to save your eyes.",
            darken_page);
define_key(content_buffer_normal_keymap, "C-d", "darken-page");