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HTML

              
                <form>
	<label for="brightness">Brightness</label>
	<input type="range" id="brightness" name="brightness" min="1" max="100" value="100">
</form>
              
            
!

CSS

              
                // mixins
@mixin thumb()
	$bg1: linear-gradient(var(--p),var(--p)) 70% 50% / 20% 5% no-repeat
	$bg2: linear-gradient(var(--l2),var(--l2)) 70% 50% / 20% 15% no-repeat
	$bg3: radial-gradient(100% 100% at 50% 50%,var(--pT) 14%,var(--p) 15% 19%,var(--pT) 20%)
	border: 0
	background: $bg1, $bg2, $bg3, var(--l2)
	border-radius: 50%
	box-shadow: -0.25em 0 0.5em var(--l3), 0.25em 0 0.5em var(--l1)
	width: 1.5em
	height: 1.5em
	-webkit-appearance: none
	-moz-appearance: none
	appearance: none

// normal styles
*
	border: 0
	box-sizing: border-box
	margin: 0
	padding: 0
\:root
	font-size: calc(48px + 24 * (100vw - 320px) / (1280 - 320))
body, form
	display: flex
body, input
	font: 1em/1.5 sans-serif
body
	--l1: hsl(228,9.8%,100%)
	--l2: hsl(228,9.8%,90%)
	--l3: hsl(228,9.8%,63%)
	--p: hsl(120,90.4%,44.9%)
	--pT: hsla(120,90.4%,44.9%,0)
	background-color: var(--l2)
	height: 100vh
form, input[type=range]
	margin: auto
form
	height: 6em
input[type=range], label
	-webkit-tap-highlight-color: transparent
input[type=range]
	background-color: transparent
	border-radius: 0.75em
	box-shadow: -0.1em -0.1em 0.1em var(--l3) inset, 0.1em 0.1em 0.1em var(--l1) inset
	cursor: pointer
	transform: rotate(-90deg)
	height: 1.5em
	width: 6em
	-webkit-appearance: none
	-moz-appearance: none
	appearance: none
	&:focus
		outline: transparent
	&::-webkit-slider-thumb
		@include thumb()
	&::-moz-range-thumb
		@include thumb()
	&::-moz-focus-outer
		border: 0
label
	clip: rect(1px,1px,1px,1px)
	overflow: hidden
	position: absolute
	width: 1px
	height: 1px
              
            
!

JS

              
                document.addEventListener("DOMContentLoaded",function(){
	let slider = this.getElementById("brightness");
	slider.addEventListener("input",adjustSlider);
	adjustSlider(slider);
});
function adjustSlider(e) {
	let body = document.body,
		switchLightMin = 40,
		switchLightMax = 100,
		tar = e.target || e,
		pct = +tar.value / +tar.max,
		L1 = pct * (switchLightMax - switchLightMin) + switchLightMin,
		L2 = L1 - 10,
		L3 = L1  - 37,
		L = [L1,L2,L3],
		thumbHueMin = 0,
		thumbHueMax = 120,
		thumbHue = pct * (thumbHueMax - thumbHueMin) + thumbHueMin,
		thumbSat = 90.4,
		thumbLight = 44.9,
		thumbHSL = `${thumbHue},${thumbSat}%,${thumbLight}%`;

	// update the slider shade
	L.forEach((light,i) => {
		if (light < 0)
			light = 0;
		body.style.setProperty(`--l${i + 1}`,`hsl(228,9.8%,${light}%)`);
	});
	// update the thumb icon hue
	body.style.setProperty(`--p`,`hsl(${thumbHSL})`);
	body.style.setProperty(`--pT`,`hsla(${thumbHSL},0)`);
}
              
            
!
999px

Console