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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>

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.

!
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-.

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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 

              
                <a href="#" class="toggle-link">
	<img src="https://brm.us/avatar" class="avatar" id="avatar1" height="100" width="100" />
</a>

<div id="modal">
	<h1>About Bramus!</h1>
	
	<img src="https://brm.us/avatar" class="avatar" id="avatar2" height="100" width="100" />
	
	<div>
		<p>Bramus Van Damme is a web developer from Belgium. From the moment he discovered <code>view-source</code> at the age of 14 <em>(way back in 1997)</em>, he <strong>fell in love with the web</strong> and has been tinkering with it ever since.</p>

		<p>With his company <a href="https://www.3rds.be/">3RDS</a> he works as a <strong>freelance developer</strong>, tackling both the frontend <em>(HTML, CSS, JS)</em> and the backend <em>(PHP, MySQL)</em>. <strong>His current focus is on JavaScript, React and React Native yet his love for CSS will never fade.</strong> Not limiting himself to only part of the stack, he also knows his way around supporting technologies <em>(HTTPS, DNS, Docker, Serverless, …)</em></p>

		<p>Before launching 3RDS, Bramus worked at several web agencies in various frontend en backend roles. For seven years he also was a <strong>Lecturer Web &amp; Mobile</strong> within the study programme Professional Bachelor ICT.</p>
	</div>
</div>
!

CSS 

              
                html,
body {
	width: 100vw;
	height: 100vh;
	background: #123456;
}

* {
	box-sizing: border-box;
	margin: 0;
	padding: 0;
}

body {
	display: grid;
	place-content: center;
}

.avatar {
	background: #ccc;
	width: 6em;
	height: auto;
	contain: paint; /* <-- DON'T FORGET THIS ONE! */
}

a.toggle-link .avatar {
	border-radius: 50%;
	border: 4px solid rgb(255 255 255 / 0.5);
}
a.toggle-link:hover .avatar {
	border-color: rgb(255 255 255 / 0.8);
}

#modal {
	position: absolute;
	background: #ccc;
	border: 4px solid #000;
	border-radius: 1em;

	display: none;
	grid-gap: 1em;
	overflow: hidden;
}

@media (orientation: portrait) {
	#modal {
		top: 10vh;
		right: 20vw;
		left: 20vw;
		bottom: 10vh;
	
		grid-template-columns: 1fr;
		grid-template-rows: 60vw 3em 1fr;
		grid-template-areas:
			"avatar"
			"title"
			"content";
	}
	
	#modal > .avatar {
		width: 100%;
	border-bottom: 4px solid #000;
	}
	
	#modal > h1 {
		text-align: center;
	}
	
	#modal > div {
		padding: 0 1rem;	
	}
}

@media (orientation: landscape) {
	#modal {
		top: 15vh;
		right: 20vw;
		left: 20vw;
		bottom: 15vh;
	
		grid-template-columns: 70vh 1fr;
		grid-template-rows: 4em 1fr;
		grid-template-areas:
			"avatar title"
			"avatar content";
	}
	
	#modal > .avatar {
		align-self: start;
		width: 100%;
	border-right: 4px solid #000;
	}
}

#modal > h1 {
	grid-area: title;
	margin: 0;
	align-self: end;
}
#modal > .avatar {
	grid-area: avatar;
}
#modal > div {
	font-size: 1.25em;
	grid-area: content;
	overflow-y: scroll;
}

#modal > div > * {
	margin-bottom: 1rem;
}

.show-modal .toggle-link {
	display: none;
}
.show-modal #modal {
	display: grid;
}
!

JS 

              
                // @ref https://www.chromestatus.com/feature/5193009714954240
console.clear();

const transition = async () => {
	const modalShown = document.body.classList.contains('show-modal');
	
	if (document.documentTransition) {
		await document.documentTransition.prepare({
			rootTransition: modalShown ? "cover-down" : "cover-up",
		});
	}

	document.body.classList.toggle("show-modal");

	if (document.documentTransition) {
		await document.documentTransition
			.start().then(() => {
				console.log("transition finished");
			});
	}
}

document.querySelector("body").addEventListener("click", (e) => {
	e.preventDefault();
	e.stopPropagation();
		
	if (!document.body.classList.contains('show-modal')) {
		return;
	}
	
	if (e.target.tagName.toUpperCase() != "BODY") {
		return;
	}

	transition();
});

document.querySelector(".toggle-link").addEventListener("click", (e) => {
	e.preventDefault();
	e.stopPropagation();

	transition();
});
!
999px

Console