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CSS

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HTML 

              
                <html lang="en" >
<head>
<meta charset="UTF-8">
<title>Dark/Light Mode Pattern</title>
<link rel="stylesheet" href="style.css">
<link id="favicon" rel="icon" href="favicon-dark.svg" color="#DDD" />
<meta name="viewport" content="width=device-width, maximum-scale=1.0, minimum-scale=1.0, initial-scale=1.0, user-scalable=no" />
</head>
<body class="dark">

<div class="load-flash"></div>

<div class="mode-toggle noselect">
	<h6 class="label-dark">Dark</h6>
	<div class="toggle-switch"></div>
	<h6 class="label-light">Light</h6>
</div>

<script src="jquery.js"></script>
<script src="script.js"></script>

</body>
</html>
!

CSS 

              
                :root {
	--gray-5:#010101; /*dark*/
	--gray-10:#040404;
	--gray-15:#070808;
	--gray-20:#0D0D0E;
	--gray-25:#141516;
	--gray-30:#1E2022;
	--gray-35:#2D2F31;
	--gray-40:#404346;
	--gray-45:#5B5E62;
	--gray-50:#7C8084;
	--gray-55:#9DA1A5;
	--gray-60:#B9BDC1;
	--gray-65:#CDD1D5;
	--gray-70:#DCE0E3;
	--gray-75:#E7EAED;
	--gray-80:#EFF2F5;
	--gray-85:#F4F7FA;
	--gray-90:#F7FAFD;
	--gray-95:#FCFEFE; /*light*/
	--animate:200ms;
}
body {
	margin:0;
	padding:40px;
	color:var(--gray-40);
	font-family:"Arial";
	background:var(--gray-70);
	-webkit-font-smoothing:antialiased;
	transition:color var(--animate) ease-in-out, background var(--animate) ease-in-out;
}
body.dark {
	color:var(--gray-80);
	background:var(--gray-35);
}
h6 {
	color:var(--gray-40);
	transition:color var(--animate) ease-in-out;
}
body.dark h6 {
	color:var(--gray-80);
}
.load-flash {
	z-index:1000;
	top:0;
	left:0;
	right:0;
	bottom:0;
	position:absolute;
	background:var(--gray-35);
}
.mode-toggle {
	display:inline-flex;
	flex-direction:row;
	align-items:center;
}
.label-dark {
	letter-spacing:-0.15px;
}
.label-light {
	letter-spacing:-0.031px;
}
.mode-toggle h6,
body.dark .mode-toggle h6 {
	text-transform:uppercase;
}
.label-dark,
.label-light {
	padding:8px 12px;
	min-width:32px;
	text-align:center;
	color:var(--gray-45);
}
body.dark .label-dark,
body.dark .label-light {
	color:var(--gray-60);
}
.label-dark:hover {
	color:var(--gray-40);
}
.label-dark:active {
	color:var(--gray-5);
}
body.dark .label-dark {
	pointer-events:none;
}
body.dark .label-light:hover {
	color:var(--gray-95);
}
body.dark .label-light:active {
	color:var(--gray-65);
}
.toggle-switch {
	margin:0;
	padding:0;
	width:48px;
	height:28px;
	border:none;
	outline:none;
	overflow:hidden;
	position:relative;
	border-radius:14px;
	display:inline-block;
	background:var(--gray-40);
}
body.dark .toggle-switch {
	width:48px;
}
.toggle-switch,
.toggle-switch:before,
.toggle-switch:after {
	transition:all var(--animate) ease-in-out;
}
body.dark .toggle-switch {
	background:var(--gray-70);
}
.toggle-switch:before {
	top:4px;
	left:24px;
	content:"";
	width:20px;
	height:20px;
	display:block;
	position:absolute;
	border-radius:12px;
	background:var(--gray-70);
}
body.dark .toggle-switch:before {
	left:4px;
	background:var(--gray-35);
}
.toggle-switch:after {
	content:"";
	top:14px;
	right:2px;
	width:1px;
	height:1px;
	display:block;
	position:absolute;
	border-radius:0.5px;
	background:var(--gray-40);
}
body.dark .toggle-switch:after {
	top:-2px;
	right:2px;
	width:32px;
	height:32px;
	border-radius:16px;
	background:var(--gray-70);
}
.toggle-switch:hover,
.toggle-switch:hover:after {
	background:var(--gray-35);
}
.toggle-switch:focus,
.toggle-switch:active,
.toggle-switch:active:after {
	background:var(--gray-25);
}
body.dark .toggle-switch:hover,
body.dark .toggle-switch:hover:after {
	background:var(--gray-95);
}
body.dark .toggle-switch:focus,
body.dark .toggle-switch:active,
body.dark .toggle-switch:active:after {
	background:var(--gray-65);
}
.noselect {
	user-select:none;
	-ms-user-select:none;
	-moz-user-select:none;
	-webkit-user-select:none;
}
.disableEasingTemporarily,
.disableEasingTemporarily:after,
.disableEasingTemporarily:before {
  -o-transition-property:none!important;
  -moz-transition-property:none!important;
  -ms-transition-property:none!important;
  -webkit-transition-property:none!important;
  transition-property:none!important;
  -o-transform:none!important;
  -moz-transform:none!important;
  -ms-transform:none!important;
  -webkit-transform:none!important;
  transform:none!important;
  -webkit-animation:none!important;
  -moz-animation:none!important;
  -o-animation:none!important;
  -ms-animation:none!important;
  animation:none!important;
}
!

JS 

              
                // Full demo here: https://timsilva.com/dm/

var darkmodeactive = localStorage.getItem("darkmode");
console.log("Dark mode is: " + darkmodeactive);
function labelDark() {
  $(".toggle-switch").attr("alt", "Go light");
  $(".toggle-switch").attr("title", "Go light");
}
function goDark() {
  console.log("Dark mode is active");
  labelDark();
  $("body").addClass("dark");
  refreshFavicon();
}
function stayDark() {
  goDark();
  localStorage.setItem("darkmode", true);
  darkmodeactive = localStorage.getItem("darkmode");
  console.log("Dark mode is: " + darkmodeactive + " and it will stay dark");
}
function labelLight() {
  $(".toggle-switch").attr("alt", "Go dark");
  $(".toggle-switch").attr("title", "Go dark");
}
function goLight() {
  console.log("Light mode is active");
  labelLight();
  $("body").removeClass("dark");
  refreshFavicon();
}
function stayLight() {
  goLight();
  localStorage.setItem("darkmode", false);
  darkmodeactive = localStorage.getItem("darkmode");
  console.log("Dark mode is: " + darkmodeactive + " and it will stay light");
}
window.matchMedia("(prefers-color-scheme: dark)").addListener(e => e.matches && stayDark());
window.matchMedia("(prefers-color-scheme: light)").addListener(e => e.matches && stayLight());
$(".toggle-switch").click(function() {
  if ($("body").hasClass("dark")) {
    stayLight();
  } else {
    stayDark();
  }
});
$(".label-light").click(function() {
  if ($("body").hasClass("dark")) {
    stayLight();
  }
});
$(".label-dark").click(function() {
  if (!$("body").hasClass("dark")) {
    stayDark();
  }
});
window.onload=function() {
  if (localStorage.darkmode=="true") {
    console.log("User manually selected dark mode from a past session");
    goDark();
  } else if (localStorage.darkmode=="false") {
    console.log("User manually selected light mode from a past session");
    goLight();
  } else {
    console.log("User hasn't selected dark or light mode from a past session, dark mode has been served by default and OS-level changes will automatically reflect");
    if ($("body").hasClass("dark")) {
      labelDark();
    } else {
      labelLight();
    }
  }
};
function tempDisableAnim() {
  $("*").addClass("disableEasingTemporarily");
  setTimeout(function() {
    $("*").removeClass("disableEasingTemporarily");
  }, 20);
}
setTimeout(function() {
  $(".load-flash").css("display","none");
  $(".load-flash").css("visibility","hidden");
  tempDisableAnim();
}, 20);
$(window).resize(function() {
  tempDisableAnim();
  setTimeout(function() {
    tempDisableAnim();
  }, 0);
});
function refreshFavicon() {
  if (matchMedia('(prefers-color-scheme: dark)').matches) {
    var link = document.querySelector("link[rel*='icon']") || document.createElement('link');
    link.type = 'image/x-icon';
    link.rel = 'icon';
    link.href = 'favicon-dark.svg';
    document.getElementsByTagName('head')[0].appendChild(link);
  } else {
    var link = document.querySelector("link[rel*='icon']") || document.createElement('link');
    link.type = 'image/x-icon';
    link.rel = 'icon';
    link.href = 'favicon.svg';
    document.getElementsByTagName('head')[0].appendChild(link);
  }
}
!
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