dark / light button

HTML

<div id="toggle">
  <i class="indicator"></i>
</div>

CSS

/* http://meyerweb.com/eric/tools/css/reset/ 
   v2.0 | 20110126
   License: none (public domain)
*/

html,
body,
div,
span,
applet,
object,
iframe,
h1,
h2,
h3,
h4,
h5,
h6,
p,
blockquote,
pre,
a,
abbr,
acronym,
address,
big,
cite,
code,
del,
dfn,
em,
img,
ins,
kbd,
q,
s,
samp,
small,
strike,
strong,
sub,
sup,
tt,
var,
b,
u,
i,
center,
dl,
dt,
dd,
ol,
ul,
li,
fieldset,
form,
label,
legend,
table,
caption,
tbody,
tfoot,
thead,
tr,
th,
td,
article,
aside,
canvas,
details,
embed,
figure,
figcaption,
footer,
header,
hgroup,
menu,
nav,
output,
ruby,
section,
summary,
time,
mark,
audio,
video {
  margin: 0;
  padding: 0;
  border: 0;
  font-size: 100%;
  font: inherit;
  vertical-align: baseline;
}
/* HTML5 display-role reset for older browsers */
article,
aside,
details,
figcaption,
figure,
footer,
header,
hgroup,
menu,
nav,
section {
  display: block;
}
body {
  line-height: 1;
}
ol,
ul {
  list-style: none;
}
blockquote,
q {
  quotes: none;
}
blockquote:before,
blockquote:after,
q:before,
q:after {
  content: "";
  content: none;
}
table {
  border-collapse: collapse;
  border-spacing: 0;
}

/* start */

body {
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  background: #2b2b2b;
  transition: 0.15s;
}

body.active {
  background: #f8f8f8;
}

#toggle {
  position: relative;
  display: block;
  width: 320px;
  height: 160px;
  border-radius: 160px;
  background: #222;
  transition: 0.5s;
  cursor: pointer;
  box-shadow: inset 0 8px 60px rgba(0, 0, 0, 0.1),
    inset 0 8px 8px rgba(0, 0, 0, 0.1), inset 0 -4px 4px rgba(0, 0, 0, 0.1);
}

#toggle.active {
  background: #fff;
  box-shadow: inset 0 2px 60px rgba(0, 0, 0, 0.1),
    inset 0 2px 8px rgba(0, 0, 0, 0.1), inset 0 -4px 4px rgba(0, 0, 0, 0.05);
}

#toggle .indicator {
  position: absolute;
  top: 0;
  left: 0;
  width: 160px;
  height: 160px;
  background: linear-gradient(to bottom, #444, #222);
  border-radius: 50%;
  transform: scale(0.9);
  box-shadow: 0 8px 40px rgba(0,...

JavaScript

const body = document.querySelector('body');
const toggle = document.getElementById('toggle');
toggle.onclick = function() {
	toggle.classList.toggle('active');
  body.classList.toggle('active');
}