问如何为随机HTML设置暗模式？

EN

<script src="https://cdn.jsdelivr.net/npm/darkmode-js@1.3.4/lib/darkmode-js.min.js"></script>
<script>

  var options = {
  bottom: '64px', // default: '32px'
  right: 'unset', // default: '32px'
  left: '32px', // default: 'unset'
  time: '0.5s', // default: '0.3s'
  mixColor: '#fff', // default: '#fff'
  backgroundColor: '#fff',  // default: '#fff'
  buttonColorDark: '#100f2c',  // default: '#100f2c'
  buttonColorLight: '#fff', // default: '#fff'
  saveInCookies: false, // default: true,
  label: '' // default: ''
}

const darkmode = new Darkmode(options);
darkmode.showWidget();

</script>

.dark .item {
    background: black;
}
.light .item {
    background: white;
}

function lightOrDark(color) {

    // Variables for red, green, blue values
    var r, g, b, hsp;

    // Check the format of the color, HEX or RGB?
    if (color.match(/^rgb/)) {

        // If HEX --> store the red, green, blue values in separate variables
        color = color.match(/^rgba?\((\d+),\s*(\d+),\s*(\d+)(?:,\s*(\d+(?:\.\d+)?))?\)$/);

        r = color[1];
        g = color[2];
        b = color[3];
    } 
    else {

        // If RGB --> Convert it to HEX: http://gist.github.com/983661
        color = +("0x" + color.slice(1).replace( 
        color.length < 5 && /./g, '$&$&'));

        r = color >> 16;
        g = color >> 8 & 255;
        b = color & 255;
    }

    // HSP (Highly Sensitive Poo) equation from http://alienryderflex.com/hsp.html
    hsp = Math.sqrt(
    0.299 * (r * r) +
    0.587 * (g * g) +
    0.114 * (b * b)
    );

    // Using the HSP value, determine whether the color is light or dark
    if (hsp>127.5) {

        return 'light';
    } 
    else {

        return 'dark';
    }
}


function getStyle(el, styleProp) {
  var value, defaultView = (el.ownerDocument || document).defaultView;
  // W3C standard way:
  if (defaultView && defaultView.getComputedStyle) {
    // sanitize property name to css notation
    // (hypen separated words eg. font-Size)
    styleProp = styleProp.replace(/([A-Z])/g, "-$1").toLowerCase();
    return defaultView.getComputedStyle(el, null).getPropertyValue(styleProp);
  } else if (el.currentStyle) { // IE
    // sanitize property name to camelCase
    styleProp = styleProp.replace(/\-(\w)/g, function(str, letter) {
      return letter.toUpperCase();
    });
    value = el.currentStyle[styleProp];
    // convert other units to pixels on IE
    if (/^\d+(em|pt|%|ex)?$/i.test(value)) { 
      return (function(value) {
        var oldLeft = el.style.left, oldRsLeft = el.runtimeStyle.left;
        el.runtimeStyle.left = el.currentStyle.left;
        el.style.left = value || 0;
        value = el.style.pixelLeft + "px";
        el.style.left = oldLeft;
        el.runtimeStyle.left = oldRsLeft;
        return value;
      })(value);
    }
    return value;
  }
}






function switch_color(el) {
  const switchable_attrs = "color backgroundColor".split(' '); // add more properties here
  for (let i in switchable_attrs) {
    let attr = switchable_attrs[i];
    let color = getStyle(el, attr);
    console.info(attr, color, el);
    if (color == "")
        continue;
    try {
        el.style[attr] = colorsys.stringify(colorsys.darken(colorsys.parseCss(color), lightOrDark(color) == "dark" ? -0.5 : 0.5));
        console.info("Color changed from " + color + " to " + el.style[attr]);
    } catch(e) {
        console.warn("Cannot switch color: " + color, e, el);
    }
  }

  for (let i = 0; i < el.children.length; i++) {
    switch_color(el.children[i]);
  }
}

let div = document.getElementById('the-div');
switch_color(div);

<!-- Theme Functions JS -->
<script type='text/javascript'>
//<![CDATA[
function retheme() {
  var cc = document.body.className;
  if (cc.indexOf("darktheme") > -1) {
    document.body.className = cc.replace("darktheme", "");
    if (opener) {opener.document.body.className = cc.replace("darktheme", "");}
    localStorage.setItem("preferredmode", "light");
  } else {
    document.body.className += " darktheme";
    if (opener) {opener.document.body.className += " darktheme";}
    localStorage.setItem("preferredmode", "dark");
  }
}
(
function setThemeMode() {
  var x = localStorage.getItem("preferredmode");
  if (x == "dark") {
    document.body.className += " darktheme";
  }
})();
//]]>
</script>

<!-- theme switch is a button icon adjust this as your icon stylesheet -->
#theme-switch{font-size:20px;position:absolute;top:0;right:35px;z-index:19}
<!-- Here is your stylesheet for dark mode editd these colors and style name except body darktheme -->
body.darktheme{color:#fff;background-color:#000}
body.darktheme .your-element-name{color:#fff;background-color:#000}
body.darktheme .lin-element-name a{color:#fff;background-color:#000}
body.darktheme #your-element-name{color:#fff;background-color:#000}
body.darktheme your-element-name ul li a{color:#fff;background-color:#000}

<div id='theme-switch'>
<a class='fa fa-adjust' href='javascript:void(0);' onclick='retheme()' title='Change Theme'/>
    </div>