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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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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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Packages

Add Packages

Search for and use JavaScript packages from npm here. By selecting a package, an import statement will be added to the top of the JavaScript editor for this package.

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Using packages here is powered by esm.sh, which makes packages from npm not only available on a CDN, but prepares them for native JavaScript ESM usage.

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HTML 

              
                <!-- horizontal progress bars -->
<div class="progress-bar horizontal top"></div>
<div class="progress-bar horizontal bottom"></div>

<!-- vertical progress bars -->
<div class="progress-bar vertical left"></div>
<div class="progress-bar vertical right"></div>

<!-- display stuff, ignore below this line -->
<div class="display-content">
	<h1>Scrolling Progress Bars</h1>
</div>

<div class="scroll"></div>
!

CSS 

              
                .progress-bar {
	display: block;
	width: 100%;
	height: 10px;
	position: fixed;
	z-index: 50;
	// this is the important line!
	// javascript controls the --scroll variable
	// "to right" can be changed to "to left" if you want to go the other way (example below)
	background: linear-gradient(to right, #CC9933 var(--scroll), transparent 0);
	background-repeat: no-repeat;
	
	&.horizontal.top {
		top: 0;
		left: 0;
	}
	
	&.horizontal.bottom {
		top: auto;
		bottom: 0;
		background: linear-gradient(to left, #CC9933 var(--scroll), transparent 0);
	}
	
	&.vertical.left {
		width: 10px;
		height: 100vh;
		top: 0;
		left: 0;
		background: linear-gradient(to bottom, #CC9933 var(--scroll), transparent 0);
	}
	
	&.vertical.right {
		width: 10px;
		height: 100vh;
		top: 0;
		right: 0;
		background: linear-gradient(to top, #CC9933 var(--scroll), transparent 0);
	}
}


// display stuff, ignore below this line
@import url('https://fonts.googleapis.com/css2?family=Montserrat:wght@900&display=swap');

body {
	background: #2b2a26;
}

.display-content {
	display: flex;
	width: 100%;
	height: 100vh;
	align-items: center;
	justify-content: center;
	
	h1 {
		color: #fff;
		font-family: Montserrat, sans-serif;
		font-size: 34px;
		text-transform: uppercase;
	}
}

.scroll {
	height: 3000px;
}
!

JS 

              
                var h = document.documentElement,
	 b = document.body,
	 st = 'scrollTop',
	 sh = 'scrollHeight',
	 htop = document.querySelector('.progress-bar.horizontal.top'),
	 hbot = document.querySelector('.progress-bar.horizontal.bottom'),
	 vleft = document.querySelector('.progress-bar.vertical.left'),
	 vright = document.querySelector('.progress-bar.vertical.right'),
	 scroll;

document.addEventListener('scroll', function() {
	console.log(h, b);
	// let's calculate the scroll position
	// ( body.scrollTop / ( body.scrollHeight - document.height ) ) * 100
	// multiplying by 100 here gives us a percent value
	scroll = ( h[st] || b[st] ) / ( ( h[sh] || b[sh] ) - h.clientHeight ) * 100;
	
	// set our variable for CSS to use
	htop.style.setProperty('--scroll', scroll + '%');
	hbot.style.setProperty('--scroll', scroll + '%');
	vleft.style.setProperty('--scroll', scroll + '%');
	vright.style.setProperty('--scroll', scroll + '%');
});
!
999px

Console