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HTML

About HTML Preprocessors

HTML preprocessors can make writing HTML more powerful or convenient. For instance, Markdown is designed to be easier to write and read for text documents and you could write a loop in Pug.

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Adding Classes

In CodePen, whatever you write in the HTML editor is what goes within the <body> tags in a basic HTML5 template. So you don't have access to higher-up elements like the <html> tag. If you want to add classes there that can affect the whole document, this is the place to do it.

About the <head>

In CodePen, whatever you write in the HTML editor is what goes within the <body> tags in a basic HTML5 template. If you need things in the <head> of the document, put that code here.

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Insecure Resource

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CSS

About CSS Preprocessors

CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.

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CSS Base

About CSS Base

It's a common practice to apply CSS to a page that styles elements such that they are consistent across all browsers. We offer two of the most popular choices: normalize.css and a reset. Or, choose Neither and nothing will be applied.

Vendor Prefixing

About Vendor Prefixing

To get the best cross-browser support, it is a common practice to apply vendor prefixes to CSS properties and values that require them to work. For instance -webkit- or -moz-.

We offer two popular choices: Autoprefixer (which processes your CSS server-side) and -prefix-free (which applies prefixes via a script, client-side).

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JavaScript

About JavaScript Preprocessors

JavaScript preprocessors can help make authoring JavaScript easier and more convenient.

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Babel includes JSX processing.

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HTML 

              
                - let lyr_data = { top: 'source', bottom: 'destination' };
- let lyr_ent = Object.entries(lyr_data);
- let lyr_val = Object.values(lyr_data);
- let lyr_n = lyr_ent.length;
- let mod_data = {
- 	hue: [0, 1, 1], 
- 	saturation: [1, 0, 1], 
- 	luminosity: [1, 1, 0], 
- 	color: [0, 0, 1]
- };
- let mod_kys = Object.keys(mod_data);
- let mod_ent = Object.entries(mod_data);
- let mod_n = mod_ent.length;
- let mod = mod_ent[mod_n - 1][0];
- let hsl_data = {
- 	h: { max: 360, val: 'rand', uni: '°' }, 
- 	s: { val: 100, uni: '%' }, 
- 	l: { uni: '%' }
- };
- let hsl_kys = Object.keys(hsl_data);
- let hsl_ent = Object.entries(hsl_data);
- let hsl_n = hsl_ent.length;
- let hsl_str = hsl_kys.map((c, i) => `--${c}: var(--${c}${mod_data[mod][i]})`).join('; ');
- let sub_str = hsl_kys.map((c, i) => `--sub-${c}: '${lyr_val[mod_data[mod][i]].charAt(0)}'`).join('; ');
- let sel_str = hsl_kys.map((c, i) => `--sel-${c}: ${mod_data[mod][i]}`).join('; ');

body.pwrap(style=`--mod: ${mod}; ${sel_str}` data-hsl=hsl_kys.join(' ') data-lyr=lyr_val.map(c => c.charAt(0)).join(' '))
	section.i.pwrap
		- for(let i = 0; i < lyr_n; i++)
			article(style=hsl_kys.map(c => `--${c}: var(--${c}${i})`).join('; '))
				h3 #{lyr_ent[i][0]} layer 
					span (#{lyr_val[i]})
				form
					- for(let j = 0; j < hsl_n; j++) {
						- let c = hsl_ent[j];
						- let m = c[1].max || 100;
						- let v = c[1].val === 'rand' ? Math.round(Math.random()*m) : c[1].val;
						div(role='group' style=`--max: ${m}; --val: var(--${c[0]}); --sel: var(--sel-${c[0]})`)
							label(for=`${c[0]}${i}`) #{c[0]}
								sub #{lyr_val[i].charAt(0)}
							input(id=`${c[0]}${i}` type='range' max=c[1].max value=v)
							output(for=`${c[0]}${i}` data-unit=c[1].uni || '')
					- }
				.box(id=`i${i}`)
	section.o
		article#o0
			h3 CSS blending
			.box
			pre
				span.token--prop mix-blend-mode
				span.token--punc :
				span.token--val.ctrl
					button(aria-haspopup='true' aria-expanded='false' aria-controls='pop')
						output(for=mod_kys.join(' ')).token--keyw #{mod}
					form#pop
						- for(let i = 0; i < mod_n; i++) {
							- let c = mod_ent[i];
							input(type='radio' name='mod' id=`mod${i}` value=c[0] data-v=`${c[1].join(' ')}` checked=c[0] === mod)
							label(for=`mod${i}` style=`--idx: ${i}`) #{c[0]}
						- }
		article#o1(style=`${hsl_str}; ${sub_str}`)
			h3 HSL approximation
			.box
			pre
				span.token--prop background
				span.token--punc :
				span.token--val
					span.token--func hsl
					span.token--punc (
					span.token--args
						- for(let i = 0; i < hsl_n; i++) {
							if i > 0
								span.token--punc ,
							span.token--arg(style=`--sub: var(--sub-${hsl_kys[i]})`) #{hsl_kys[i]}
								sub
						- }
					span.token--punc )
!

CSS 

              
                $u: 1.25;
$r: 5em;
$s: 2*$r;
$g: #000 #1b1d22 #22242a #323741 #484d5a #7b849c #c4c4c4 #fff;
$c: #bf79f0 #fb678c #fb8c6c #eaa753;
$t: .3s;

$label-w: 1.25em;

$value-w: 2.5em;
$value-b: .3em;
$value-r: 5px;
$value-a: 70deg;
$value-e: 5deg;

$thumb-d: 1em;
$thumb-r: .5*$thumb-d;
$thumb-f: .5;
$thumb-l: 3px;

$track-m: .5*$value-w - $thumb-r + .2*$value-b;
$track-w: $s - 2*$track-m;
$track-h: 6px;
$track-r: .5*$track-h;

// wide --wide: 1
$break-0: 2*(2*($s + $label-w + $value-w + $value-b + .5*$track-m) + 3*$track-m) + 3*$track-m;
// narr --wide: 0
$break-1: 2*(2*$s + 3*$track-m) + 3*$track-m;
// wide --wide: 1
$break-2: 2*($s + $label-w + $value-w + $value-b + .5*$track-m + 2*$track-m) + 3*$track-m;
// narr --wide: 0
$break-3: 2*$s + 3*$track-m + 3*$track-m;
// wide --wide: 1
$break-4: $s + $label-w + $value-w + $value-b + .5*$track-m + 4*$track-m;
// narr --wide: 0

@mixin track() {
	border: none;
	width: 100%; height: $track-h;
	border-radius: $track-r;
	background: 
		radial-gradient(circle at var(--pos), 
			transparent calc(#{$thumb-f}*#{$thumb-r} + #{$thumb-l}), 
			nth($g, 5) calc(#{$thumb-f}*#{$thumb-r} + #{$thumb-l} + 1px))
}

@mixin thumb($f: 0) {
	margin-top: calc(#{$f}*(#{$track-r} - #{$thumb-r}));
	border: none;
	width: $thumb-d; height: $thumb-d;
	border-radius: 50%;
	transform: scale(calc(var(--not-hl)*#{$thumb-f} + var(--hl)));
	background: nth($c, 4);
	transition: transform $t;
	cursor: ew-resize
}

* { margin: 0; border: none; padding: 0; background: transparent; color: inherit; font: inherit }

body, section, article, form { display: grid }

body {
	overflow-x: hidden;
	padding: $track-m;
	background: nth($g, 3);
	color: nth($g, 6);
	font: clamp(.625em, 6.25vw, #{$u*1em})/ 1.25 raleway, 
		trebuchet ms, verdana, arial, sans-serif
}

.pwrap {
	grid-gap: $track-m;
	
	> :not(.pwrap) {
		padding: $track-m;
		border-radius: 5px;
		box-shadow: 0 0 1px 1px nth($g, 5);
		background: nth($g, 2)
	}
}

section {
	grid-template-columns: repeat(auto-fit, minmax(calc(#{$s} + #{2*$track-m}), 1fr))
}

article {
	--i: var(--parity, 1);
	--not-i: calc(1 - var(--i));
	grid-gap: $track-m;
	align-content: start;
	
	&:nth-child(odd) { --parity: 0 }
	
	.i & {
		grid-template-columns: repeat(auto-fit, minmax(Max(#{$s}, calc(50% - 2*#{$track-m})), 1fr));
		direction: var(--parity, rtl);
		
		form { grid-gap: .675em }
	}
}

h3, form { direction: ltr }

h3 {
	grid-column: 1/ -1;
	font-weight: 700
}

form, pre { font-family: ubuntu mono, consolas, monaco, monospace }

[role='group'] {
	--j: var(--wide, 1);
	--not-j: calc(1 - var(--j));
	--hl: 0;
	--not-hl: calc(1 - var(--hl));
	--used: calc(1 - Max(calc(var(--sel) - var(--i)), calc(var(--i) - var(--sel))));
	--pos: calc(#{$thumb-r} + var(--val)/var(--max)*(100% - #{$thumb-d}));
	display: grid;
	align-items: center;
	grid-gap: 0 .25*$track-m;
	grid-template-columns: calc(var(--j)*#{$label-w} + var(--not-j)*100%) var(--wide, 1fr #{$value-w + $value-b});
	z-index: var(--hl);
	padding: calc(var(--not-j)*.5*#{$track-m}) $track-m;
	border-radius: 5px;
	box-shadow: 
		0 0 0 calc(var(--used)*1px) nth($c, 1), 
		0 0 0 calc(var(--used)*4px) rgba(nth($c, 1), .35);
	
	* {
		filter: Saturate(var(--hl));
		transition: filter $t
	}
	
	[for] { text-align: center }
	
	label { width: $label-w }
	
	&:focus-within { --hl: 1 }
	
	@media (min-width: $u*$break-1) and (max-width: $u*$break-0), 
				 (min-width: $u*$break-3) and (max-width: $u*$break-2), 
				 (max-width: $u*$break-4) { --wide: 0 }
}

sub { font-size: .675em }

[type='range'] {
	&, &::-webkit-slider-runnable-track, 
	&::-webkit-slider-thumb { -webkit-appearance: none }
	
	grid-column: calc(1 + var(--j));
	min-width: $track-w;
	height: $thumb-d;
	cursor: pointer;
	
	&:focus { outline: none }
	
	&::-webkit-slider-runnable-track { @include track }
  &::-moz-range-track { @include track }
	
	&::-webkit-slider-thumb { @include thumb(1) }
  &::-moz-range-thumb { @include thumb }
	
	+ output {
		--xy: calc(var(--not-j)*50%) calc((2 - var(--j))*50%);
		display: grid;
		grid-column: calc(1 + 2*var(--j));
		position: relative;
		left: calc(var(--not-j)*var(--pos));
		margin-right: calc(var(--j)*#{-$value-b});
		margin-bottom: calc(var(--not-j)*#{-2*$value-b - $u*1em});
		border: solid $value-b transparent;
		width: $value-w;
		transform-origin: var(--xy);
		transform: 
			translate(calc(var(--not-j)*-50%), calc(var(--not-j)*(#{-$thumb-d} - 100% - 1px))) 
			scale(calc(var(--not-j)*var(--hl) + var(--j)));
		color: nth($g, 2);
		transition: transform $t;
		counter-reset: val var(--val);
		
		&::before, &::after { grid-area: 1/ 1 }
		
		&::before {
			margin: -$value-b;
			background: 
				conic-gradient(
						from calc(var(--j)*90deg - .5*#{$value-a}) 
						at var(--xy), 
						transparent, 
						nth($c, 4) $value-e $value-a - $value-e, 
						transparent  $value-a) 
					var(--xy)/ 50% 50% no-repeat;
			content: ''
		}

		&::after {
			border-radius: $value-r;
			background: nth($c, 4);
			content: counter(val) attr(data-unit)
		}
	}
}

.box {
	--j: var(--narr, 1);
	--not-j: calc(1 - var(--j));
	--c0: HSL(var(--h0), calc(var(--s0)*1%), calc(var(--l0)*1%));
	--c1: HSL(var(--h1), calc(var(--s1)*1%), calc(var(--l1)*1%));
	padding: $r;
	background: HSL(var(--h), calc(var(--s)*1%), calc(var(--l)*1%));
	
	.o & {
		grid-row: calc(var(--not-j)*2 + var(--j)*(var(--not-i)*3 + var(--i)));
		
		@media (min-width: 545px) { --narr: 0 }
	}
	
	[id='o0'] & {
		background: linear-gradient(var(--c0), var(--c0)) var(--c1);
		background-blend-mode: var(--mod)
	}
	
	[id='o1'] & {
		background: HSL(var(--h), calc(var(--s)*1%), calc(var(--l)*1%));
	}
}

pre, span, button, label {
	display: inline-flex;
	flex-wrap: wrap;
	align-items: flex-end
}

pre { align-self: start }

.token {
	&--prop { color: nth($c, 2) }
	
	&--val { margin-right: .75em }
	
	&--func { color: nth($c, 1) }
	
	&--keyw { color: nth($c, 3) }
	
	&--arg { color: nth($c, 4) }
	
	&--punc + :not(&--args) {
		&::before { content: ' ' }
	}
	
	&--arg {
		sub::after { content: var(--sub) }
	}
}

.ctrl { position: relative }

[aria-controls] {
	--hl: 0;
	padding: 0 .25em;
	border-radius: 5px;
	box-shadow: 0 0 0 calc(var(--hl)*2px) nth($c, 3);
	font-weight: 900;
	cursor: pointer;
	
	&:focus { outline: none }
	&:focus, &:hover { --hl: 1 }
}

[id='pop'] {
	--exp: 0;
	--not-exp: calc(1 - var(--exp));
	display: grid;
	grid-auto-flow: dense;
	grid-template-columns: max-content 1em;
	overflow: hidden;
	position: absolute;
	bottom: calc(100% + .5em); left: 0;
	padding: .5em;
	border-radius: 5px;
	transform-origin: 0 100%;
	transform: 
		perspective(35em)
		//rotatex(calc(var(--not-exp)*90deg)) 
		translate(calc(var(--not-exp)*-50%));
	opacity: var(--exp);
	box-shadow: 0 0 0 1px nth($g, 5), 
		4px 4px 33px rgba(nth($g, 1), .35), 
		inset 0 0 13px rgba(nth($g, 1), .2);
	background: nth($g, 3);
	transition: $t calc(var(--not-exp)*#{$t});
	transition-property: opacity, transform;
	
	[aria-expanded='true'] + & { --exp: 1 }
}

[type='radio'] {
	grid-column: 2;
	place-self: center;
	opacity: .0001;
	
	+ label {
		--sel: 0;
		position: relative;
		transform: 
			translate(calc(var(--not-exp)*50%));
		opacity: var(--exp);
		transition: inherit;
		transition-delay: calc(var(--exp)*#{$t} + (var(--idx) - 1)*.05s);
		cursor: pointer;
		
		&::after {
			display: grid;
			place-content:center;
			position: absolute;
			left: 100%; top: 0;
			width: 1em; height: 100%;
			opacity: var(--sel);
			content: '✔'
		}
	}
	
	&:checked + label { --sel: 1 }
}
!

JS 

              
                const _BODY = document.body, 
			_O1 = document.getElementById('o1'), 
			HSL = _BODY.dataset.hsl.split(' '), 
			LYR = _BODY.dataset.lyr.split(' '), 
			_BTN = document.querySelector('button[aria-controls]');

function setVal(_e) { _BODY.style.setProperty(`--${_e.name || _e.id}`, _e.value) }

function toggleExp(val) {
	_BTN.setAttribute('aria-expanded', val || `${!(_BTN.getAttribute('aria-expanded') === 'true')}`)
}

[...document.querySelectorAll('input')].forEach(_e => setVal(_e));

addEventListener('input', e => setVal(e.target));

addEventListener('change', e => {
	let _t = e.target;
	
	if(_t.type === 'radio') {
		let _o = document.querySelector(`output[for*=${_t.value}]`), 
				v = _t.dataset.v.split(' ').map(c => + c);

		setVal(_t);
		_o.textContent = _t.value;
		HSL.forEach((c, i) => {
			_BODY.style.setProperty(`--sel-${c}`, `${v[i]}`);
			_O1.style.setProperty(`--${c}`, `var(--${c}${v[i]})`);
			_O1.style.setProperty(`--sub-${c}`, `'${LYR[v[i]]}'`)
		})
	}
})

addEventListener('click', e => toggleExp(e.target.parentNode === _BTN ? null : 'false'));
!
999px

Console