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HTML

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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

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About the <head>

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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

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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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Packages

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HTML 

              
                <button class="toggle">Toggle Disclosure Widget State</button>

<div class="disclosure-widget">
	<h1 class="disclosure-widget__headline">CSS Stickers</h1>
	<p>A set of beautiful, cute, and funny CSS stickers to showcase your love for CSS.</p>
	<p><a href="https://stickers.css-weekly.com" target="_blank">Check out CSS Stickers »</a></p>
</div>
!

CSS 

              
                body {
	margin: 0;
	padding-block: 1rem;
	padding-inline: 2rem;
	min-block-size: 100vb;
	box-sizing: border-box;
	line-height: 1.5;
	font-size: 1.2rem;
	font-family: sans-serif;
	background: linear-gradient(
		to right bottom, 
		hsl(225deg 76% 48%), 
		hsl(225deg 71% 40%), 
		hsl(220deg 40% 11%)
	);
}

a {
	color: hsl(225deg 76% 48%);
}

p {
	margin-block: 1rem;
}

code {
	white-space: nowrap;
}

.notice { 
	max-inline-size: 30rem;
	margin-inline: auto;
	margin-block: 0rem 3rem;
	color: hsl(0 100% 95%);
	text-align: center;
	text-wrap: balance;
	display: no<p class="notice">…</p>ne; 
	background: hsl(0 70% 30% / 0.8);
	border: 1px solid hsl(0 70% 35% / 0.8);
	padding: 2rem;
	border-radius: 0.5rem;
}

.disclosure-widget[open] + .notice {
	margin-block-start: 2rem;
}

.toggle {
	position: relative;
	display: block;
	width: auto;
	margin-block: 1rem 2rem;
	margin-inline: auto;
	padding-block: 0.8rem;
	padding-inline: 1.5rem;
	color: hsl(261deg 100% 25%);
	text-decoration: none;
	cursor: pointer;
	background: hsl(261deg 100% 95%);
	border: 1px solid hsl(0 0% 10%);
	border-radius: 0.5rem;
	transition: all 0.4s ease-in-out;
}

.toggle:hover {
	color: hsl(261deg 100% 15%);
	background: hsl(261deg 100% 100%);
}

.toggle:active {
	inset-block-start: 0.1rem;
	inset-inline-start: 0.1rem;
}

.disclosure-widget {
	position: relative;
	max-inline-size: 30rem;
	margin-block: 2rem 0;
	margin-inline: auto;
	padding-block: 0;
	padding-inline: 2rem;
	overflow: hidden;
	border-radius: 0.5rem;
	background-image: linear-gradient(
		to top left,
		hsl(260 80% 80%) 0,
		hsl(0 100% 95%)
	);
}

.disclosure-widget__headline { 
	margin-block-start: 0;
	margin-block-end: 1rem;
	line-height: 1;
	color: hsl(225deg 71% 20%);
}

.disclosure-widget > :first-child {
	margin-block-start: 2.5rem;
}

.disclosure-widget > :last-child {
	margin-block-end: 2.5rem;
}

/* Demo Code */
.disclosure-widget {
	height: 0;
	transition: all 0.7s ease-in-out;
}
	
.disclosure-widget[open] {
	/* Custom styles for the open state. */
}
!

JS 

              
                // The video guide: https://youtu.be/1VsMKz4Zweg

// Get page elements
const toggle = document.querySelector('.toggle');
const widget = document.querySelector('.disclosure-widget');

// Widget State
let isOpen = false;

// Get the widget open/closed height
// 1. Get the closed state height (could be different from 0, based on CSS)
// 2. Set the 'height' to auto to force content-sized dimensions
// 3. Store the open widget height in 'px' units
// 4. Return the widget to its intial height
// This is necessary but suboptimal as if forces the browser to do extra layouts.
const closedHeight = widget.style.height;
widget.style.height = 'auto';
const openHeight = widget.offsetHeight + 'px';
widget.style.height = closedHeight;

// Toggle the open/close widget state on click of the 'toggle' button
toggle.addEventListener('click', (e) => {
	let height = isOpen ? closedHeight : openHeight;
	
	widget.toggleAttribute('open');
	widget.style.height = height;
	isOpen = !isOpen;
});
!
999px

Console