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<h1 class="challenge-title">Switch Dark</h1>
<h2 class="challenge-subtitle">#28ComponentsOfFebruaryDay4</h2>
<p class="challenge-part-of">Part of <a href="https://codepen.io/collection/DQRePJ" target="_blank">28 Components of February</a> collection.</p>

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<div class="container">
	<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 801.90879 212.81068">
		<path class="letter letter-s" d="M84.34338,101.49515A33.29437,33.29437,0,0,0,71.60244,90.145,93.68539,93.68539,0,0,0,50.56631,82.57a103.54316,103.54316,0,0,1-12.24419-3.70056c-2.75677-1.09279-4.64434-2.21045-5.63785-3.37783a6.37588,6.37588,0,0,1-1.515-4.32146,6.91671,6.91671,0,0,1,3.45225-6.10959c2.30974-1.51512,5.56327-2.26017,9.76058-2.26017a47.08562,47.08562,0,0,1,14.05718,2.30974,76.56409,76.56409,0,0,1,13.337,5.464,7.93816,7.93816,0,0,0,1.34125.24845c1.36595,0,2.558-.81963,3.52668-2.434l7.873-13.21284a4.73462,4.73462,0,0,0,.8445-2.558c0-1.44054-.89407-2.65748-2.65749-3.62613A79.01559,79.01559,0,0,0,65.17,41.59044,70.73539,70.73539,0,0,0,44.38214,38.4362q-11.8841,0-20.4898,4.29675a32.04745,32.04745,0,0,0-13.11355,11.3997,28.266,28.266,0,0,0-4.47047,15.3487c0,7.02867,1.41568,12.81553,4.2966,17.33572A30.79638,30.79638,0,0,0,23.023,97.74488a104.56264,104.56264,0,0,0,21.235,7.3764q10.05844,2.57055,14.67808,5.29011c3.0548,1.813,4.59463,4.17245,4.59463,7.07823,0,3.00523-1.49011,5.1411-4.47048,6.43248-3.00507,1.29152-7.40111,1.93729-13.23754,1.93729q-14.0449,0-31.1446-8.84166a5.95935,5.95935,0,0,0-2.68234-.72019,3.94661,3.94661,0,0,0-3.40254,2.16073L.84434,132.16771A4.37842,4.37842,0,0,0,0,134.7259c0,1.366.79477,2.50847,2.409,3.37768a110.90286,110.90286,0,0,0,19.64546,8.44434,75.5915,75.5915,0,0,0,23.76819,3.82471q19.8936,0,31.41761-8.12146c7.67442-5.43912,11.524-13.26241,11.524-23.5446C88.76428,111.85178,87.29889,106.08978,84.34338,101.49515Z" />
		<path class="letter letter-c"  d="M185.89833,117.01773a3.11153,3.11153,0,0,0-2.65748-1.34109,4.74291,4.74291,0,0,0-2.1856.6209,34.01759,34.01759,0,0,1-22.4518,8.36976,28.08445,28.08445,0,0,1-14.90167-4.14774,30.59928,30.59928,0,0,1-10.80366-11.07682,30.583,30.583,0,0,1-.04972-30.15109,29.3511,29.3511,0,0,1,10.72923-10.90309A28.66773,28.66773,0,0,1,158.50416,64.39q11.99574,0,22.6754,8.59335a3.79994,3.79994,0,0,0,2.18544.74506,3.14506,3.14506,0,0,0,2.65748-1.58955l9.71086-14.77753a4.43569,4.43569,0,0,0,.84464-2.43389,3.49507,3.49507,0,0,0-1.34124-2.55819,57.4927,57.4927,0,0,0-37.10518-13.58529A56.19963,56.19963,0,0,0,109.50239,66.501a55.52079,55.52079,0,0,0,.04972,55.90614,56.4539,56.4539,0,0,0,20.51466,20.31593,54.95733,54.95733,0,0,0,28.18894,7.52542,53.92275,53.92275,0,0,0,19.695-3.651,57.63162,57.63162,0,0,0,17.0377-10.18275,3.43813,3.43813,0,0,0,1.58954-2.78163,3.3049,3.3049,0,0,0-.84464-2.1856Z" />
		<path class="letter letter-r"  d="M302.92613,48.37065a31.82331,31.82331,0,0,0-11.69771-7.277,42.79329,42.79329,0,0,0-14.728-2.53333A37.48575,37.48575,0,0,0,258.37,43.22955a40.447,40.447,0,0,0-14.25591,12.66652l-2.18529-11.8966c-.32318-1.44039-1.46555-2.16073-3.40284-2.16073H223.12765a3.61216,3.61216,0,0,0-2.60791.89421,3.42219,3.42219,0,0,0-.89376,2.48361v98.351c0,2.35946,1.1175,3.52668,3.37737,3.52668h19.422c2.25987,0,3.37768-1.16722,3.37768-3.52668V87.66142A24.617,24.617,0,0,1,249.37961,74.697a25.98291,25.98291,0,0,1,9.7107-9.413A26.94127,26.94127,0,0,1,272.477,61.83179a30.42634,30.42634,0,0,1,8.74237,1.34124,23.33961,23.33961,0,0,1,7.87316,3.99858l.8692.7202a2.21254,2.21254,0,0,0,1.689.6209,2.77147,2.77147,0,0,0,2.65733-1.5894L303.423,52.866a4.01436,4.01436,0,0,0,.72-2.18559A2.66674,2.66674,0,0,0,302.92613,48.37065Z" />
		<path class="letter letter-p"  d="M425.34349,65.95467a49.8223,49.8223,0,0,0-18.00619-19.993,47.38951,47.38951,0,0,0-25.95393-7.277,45.36306,45.36306,0,0,0-21.28443,5.0168,44.62606,44.62606,0,0,0-16.0692,14.25591l-2.18529-14.05718c-.22374-1.31639-1.16723-1.962-2.78194-1.962H323.06819a3.16363,3.16363,0,0,0-2.38417.96849,3.69315,3.69315,0,0,0-.89406,2.55819V195.59927a3.58675,3.58675,0,0,0,.89406,2.53318,3.09477,3.09477,0,0,0,2.38417.9935h19.52146a3.62279,3.62279,0,0,0,2.60762-.91892,3.53322,3.53322,0,0,0,.89406-2.60776l-.22344-62.21447a44.59084,44.59084,0,0,0,15.62172,12.4925,45.80562,45.80562,0,0,0,20.01806,4.37118,47.41908,47.41908,0,0,0,25.82963-7.277,50.05535,50.05535,0,0,0,18.00619-20.01791,61.88709,61.88709,0,0,0,6.48219-28.48711A61.9902,61.9902,0,0,0,425.34349,65.95467Zm-22.97342,43.662a29.36167,29.36167,0,0,1-10.80365,10.90294,28.66348,28.66348,0,0,1-14.90168,4.02344,30.38909,30.38909,0,0,1-15.39857-4.02344,29.66308,29.66308,0,0,1-11.10168-10.85338,28.96016,28.96016,0,0,1-4.07316-15.07554,30.2666,30.2666,0,0,1,30.44911-30.449,28.8657,28.8657,0,0,1,14.97626,4.073,29.8282,29.8282,0,0,1,10.85337,11.02724,30.37143,30.37143,0,0,1,3.99858,15.34871A29.58846,29.58846,0,0,1,402.37007,109.61662Z" />
		<path class="letter letter-t"  d="M482.64029,85.78243v-18.735h7.43647a1.8078,1.8078,0,0,0,1.65582-1.08225L501.656,43.31854a.985.985,0,0,0-.90221-1.38036H482.64029V3.26831a3.80328,3.80328,0,0,0-.64576-2.30974A2.2704,2.2704,0,0,0,480.107.11408a5.97933,5.97933,0,0,0-1.34125.2483l-19.76946,7.749a3.77035,3.77035,0,0,0-2.78133,3.87443V41.93818h-11.8966c-2.161,0-3.25368,1.09279-3.25368,3.27838V63.76908c0,2.18559,1.09265,3.27838,3.25368,3.27838h12.0206v77.57779a2.79643,2.79643,0,0,0,5.33751,1.16746L482.26024,87.52A4.162,4.162,0,0,0,482.64029,85.78243Z" />
		<path class="letter letter-t" d="M511.54905,64.355a17.15221,17.15221,0,0,0-.9184,5.53729v74.04789a3.29874,3.29874,0,0,0,.84465,2.43389,3.36385,3.36385,0,0,0,2.43389.84434h19.8689c2.11071,0,3.15424-1.09279,3.15424-3.27823V67.04746h25.109a3.27854,3.27854,0,0,0,3.27854-3.27854V45.21672a3.27854,3.27854,0,0,0-3.27854-3.27854h-25.109V2.01a2.00728,2.00728,0,0,0-3.83284-.83458Z" />
		<path class="letter letter-a"  d="M664.81351,57.83321a38.83426,38.83426,0,0,0-16.839-14.18133q-10.87839-4.99216-25.30817-4.96723a89.43069,89.43069,0,0,0-20.41522,2.409A58.85833,58.85833,0,0,0,584.717,47.89876q-3.50214,1.93728-3.50229,4.84307a4.791,4.791,0,0,0,.472,2.18559L587.49834,66.203c.4969,1.21694,1.58985,1.81314,3.27853,1.81314a7.96388,7.96388,0,0,0,3.02994-.72035,48.72534,48.72534,0,0,1,13.41157-4.9175,70.1686,70.1686,0,0,1,15.34885-1.76342q9.57412,0,15.746,5.63785,6.18432,5.66271,6.18417,15.22455v5.09138l-35.88838.12415q-17.32283.11187-26.798,7.64957-9.4627,7.52541-9.46241,22.30279a31.33132,31.33132,0,0,0,18.6271,29.60477,46.95661,46.95661,0,0,0,20.06717,4.12273q12.96485,0,22.1788-4.32146a38.283,38.283,0,0,0,14.80253-11.69787l1.813,10.6795a2.81759,2.81759,0,0,0,1.04292,1.44054,2.68619,2.68619,0,0,0,1.76327.6209h14.77768a3.236,3.236,0,0,0,2.48361-.96864,3.704,3.704,0,0,0,.91892-2.6822V79.54C670.82365,71.21991,668.81178,63.96781,664.81351,57.83321Zm-20.31609,49.22521a19.49911,19.49911,0,0,1-3.502,11.30041,24.15929,24.15929,0,0,1-9.537,7.99731,29.47777,29.47777,0,0,1-13.01411,2.90578q-8.38219,0-14.08219-3.94886-5.7-3.91186-5.68757-10.10832a9.65451,9.65451,0,0,1,3.502-7.94759c2.35961-1.91243,5.66271-2.85621,9.95931-2.85621h32.36154Z" />
		<path class="letter letter-g"  d="M796.99129,156.60652a30.66641,30.66641,0,0,0-13.88362-11.02724c-5.98528-2.5582-13.039-3.82471-21.21014-3.82471H730.35577a16.86663,16.86663,0,0,1-8.91608-2.11116c-2.285-1.41568-3.45226-3.25353-3.45226-5.53841a9.36489,9.36489,0,0,1,1.391-5.09138,8.94733,8.94733,0,0,1,3.82486-3.27838,46.58653,46.58653,0,0,0,19.04911,4.02344,48.41889,48.41889,0,0,0,23.76834-5.83658,42.64057,42.64057,0,0,0,16.54064-16.11862,44.2303,44.2303,0,0,0,5.88615-23.172,37.83732,37.83732,0,0,0-6.53191-21.086h10.90309A4.77158,4.77158,0,0,0,796.39524,62.13a4.56111,4.56111,0,0,0,1.39067-3.32811v-12.12a4.60906,4.60906,0,0,0-1.31609-3.52669,5.30908,5.30908,0,0,0-3.65114-1.21694H760.20884a75.49474,75.49474,0,0,0-9.661-2.48362,46.61718,46.61718,0,0,0-8.04719-.89421,45.91363,45.91363,0,0,0-23.346,5.93587,42.03946,42.03946,0,0,0-16.1932,16.36707,47.807,47.807,0,0,0-5.83612,23.64389,46.77982,46.77982,0,0,0,2.55789,15.52258,43.139,43.139,0,0,0,7.27712,13.11354,22.58607,22.58607,0,0,0-9.16469,9.21426,27.58641,27.58641,0,0,0-3.328,13.46114A26.75637,26.75637,0,0,0,699.0129,151.391a29.06867,29.06867,0,0,0,12.74064,10.18276,46.0238,46.0238,0,0,0,18.60223,3.5764h31.54176c5.58813,0,9.71131.81964,12.41806,2.43389,2.70736,1.61441,4.07346,4.32147,4.07346,8.12147q0,6.55677-8.24576,10.0586-8.233,3.53919-22.55109,3.52668a130.46779,130.46779,0,0,1-20.4898-1.68884,96.91274,96.91274,0,0,1-18.08077-4.49533,6.09976,6.09976,0,0,0-1.46525-.2483,3.71036,3.71036,0,0,0-2.161.67047,3.8755,3.8755,0,0,0-1.46494,1.88757L698.218,199.59785a5.37158,5.37158,0,0,0-.34774,1.68883,4.07971,4.07971,0,0,0,.67062,2.26018,5.00781,5.00781,0,0,0,1.86271,1.63911,100.64184,100.64184,0,0,0,21.90533,5.63785,167.06428,167.06428,0,0,0,25.28331,1.98686q16.35463,0,28.68554-4.6692,12.29406-4.65678,18.97514-13.46114,6.66819-8.79216,6.65591-21.03627A29.51429,29.51429,0,0,0,796.99129,156.60652ZM724.4202,73.52965A20.9996,20.9996,0,0,1,731.995,65.7808,20.29682,20.29682,0,0,1,742.625,62.92458a21.2486,21.2486,0,0,1,18.60224,10.60507,21.42,21.42,0,0,1,2.85621,10.97753,20.45468,20.45468,0,0,1-10.60507,18.13049,22.088,22.088,0,0,1-10.97768,2.73191A20.711,20.711,0,0,1,731.871,102.588a20.32526,20.32526,0,0,1-7.50056-7.575A20.92082,20.92082,0,0,1,721.63827,84.383,21.59825,21.59825,0,0,1,724.4202,73.52965Z" />
	</svg>
</div>
!

CSS 

              
                @import url("https://fonts.googleapis.com/css2?family=Source+Sans+Pro:ital,wght@0,700;1,400&display=swap");

$purple: #9b5de5;
$magenta: #c65ccd;
$pink: #f15bb5;
$yellow: #fee440;
$blue: #00bbf9;
$aqua: #00d8e7;
$green: #00f5d4;

$default: #d1d5da;
$defaultBg: #2f363d;
$dark: #c9d1d9;
$darkBg: #0d1117;

* {
	box-sizing: border-box;
}

@mixin turnOn($color, $name) {
	@keyframes #{$name}TurnOn {
		from {
			fill: $dark;
		}
		to {
			fill: $color;
		}
	}
}

@include turnOn($purple, "purple");
@include turnOn($magenta, "magenta");
@include turnOn($pink, "pink");
@include turnOn($yellow, "yellow");
@include turnOn($blue, "blue");
@include turnOn($aqua, "aqua");

@keyframes flickerTurnOn {
	0% {
		fill: $dark;
	}

	2% {
		fill: $green;
	}
	
	8% {
		fill: $dark;
	}
	
	9% {
		fill: $green;
	}
	12% {
		fill: $dark;
	}
	
	20% {
		fill: $green;
	}
	
	25% {
		fill: $dark;
	}
	
	30% {
		fill: $green;
	}

	70% {
		fill: $dark;
	}

	72% {
		fill: $green;
	}

	77% {
		fill: $dark;
	}
	
	100% {
		fill: $green;
	}
}

.hidden {
	width: 0;
	height: 0;
	visibility: hidden;
	display: none;
	overflow: hidden;
}

html {
	font-size: 16px;
}

body {
	display: flex;
	padding: 0;
	margin: 0;
	align-items: center;
	flex-direction: column;
	min-height: 100vh;
	font-family: "Source Sans Pro", sans-serif;
	position: relative;
	&.dark {
		background-color: $darkBg;
		.challenge-title {
			color: $dark;
		}
		.challenge-subtitle {
			color: darken($dark, 50%);
		}
		.challenge-part-of {
			color: darken($dark, 50%);
			a, a:visited {
				color: darken($dark, 50%);
				&:hover, &:active {
					color: lighten(darken($dark, 50%), 10%);
				}
			}
		}
		.letter {
			fill: $dark;
		}
		.letter-s {
			animation: purpleTurnOn 0.1s linear forwards 0.2s;
		}
		.letter-c {
			animation: aquaTurnOn 0.1s linear forwards 0.6s;
		}
		.letter-r {
			animation: pinkTurnOn 0.1s linear forwards 0.4s;
		}
		.letter-p {
			animation: yellowTurnOn 0.1s linear forwards 1s;
		}
		.letter-t {
			animation: flickerTurnOn 2s linear 1.4s infinite alternate;
		}
		.letter-a {
			animation: magentaTurnOn 0.1s linear forwards 0.8s;
		}
		.letter-g {
			animation: blueTurnOn 0.1s linear forwards 1.2s;
		}
	}
}

.letter {
	fill: $default;
}

.background {
	position: absolute;
	top: 0;
	left: 0;
	width: 100%;
	min-height: 100%;
	background-color: #eeeef9;
	opacity: 0.3;
	background-image: repeating-radial-gradient(
			circle at 0 0,
			transparent 0,
			#eeeef9 20px
		),
		repeating-linear-gradient(#aa90d355, #aa90d3);
}

.challenge-title {
	text-align: center;
	padding: 0;
	margin: 1rem 0 0;
	color: $defaultBg;
	font-size: 2rem;
	font-weight: bold;
}

.challenge-subtitle {
	text-align: center;
	margin: 0;
	font-size: 1.125rem;
	font-weight: 400;
	color: $default;
}

.challenge-part-of {
	text-align: center;
	margin: 1rem 0 0;
	font-size: 0.875rem;
	color: $default;
	position: fixed;
	bottom: 1rem;
	right: 1rem;
	a,
	a:visited {
		color: $default;
		text-decoration-style: wavy;
		&:hover,
		&:active {
			color: lighten($default, 10%);
		}
	}
}

.sr-only {
	visibility: hidden;
}

.container {
	display: flex;
	align-items: center;
	justify-content: center;
	width: 500px;
	padding: 1rem;
	margin: 1rem;
}

.btn {
	background-color: transparent;
	border: 4px solid $default;
	border-radius: 12.5px;
	cursor: pointer;
	&:hover {
		.tick {
			background-color: lighten($defaultBg, 5%);
		}
	}
	&:active {
		.tick {
			background-color: darken($defaultBg, 5%);
		}
	}
	&:focus {
		outline: 1px dotted darken($defaultBg, 20%);
	}
	&.btn-switch {
		position: relative;
		width: 50px;
		&.on {
			.tick {
				.sun {
					display: none;
				}
				.moon {
					display: block;
				}
			}
		}
		&.on {
			background-color: darken($purple, 40%);
			border-color: darken($purple, 30%);
			.tick {
				background-color: $purple;
				transform: translate(100%, -50%);
			}
		}
		.tick {
			background-color: $defaultBg;
			border-radius: 50%;
			display: flex;
			align-items: center;
			justify-content: center;
			width: 30px;
			height: 30px;
			position: absolute;
			top: 50%;
			left: -4px;
			transform: translateY(-50%);
			transition: transform 0.15s ease-in-out;
			.icon {
				flex: 0 0 80%;
				height: 100%;
			}
			.sun {
				display: block;
			}
			.moon {
				display: none;
			}
		}
	}
}
!

JS 

              
                const buttonSwitch = document.querySelector('.btn-switch');
const body = document.querySelector('body');

buttonSwitch.addEventListener('click', function(e){
	this.classList.toggle('on');
	body.classList.toggle('dark')
});
!
999px

Console