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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

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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 Skypack, which makes packages from npm not only available on a CDN, but prepares them for native JavaScript ES6 import usage.

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HTML 

              
                <div id="blurryscroll" aria-hidden="true"></div>
<nav>
  <a href="#">Tours</a>
  <a href="#">Popular Destinations</a>
  <a href="#">History</a>
</nav>
<main id="content">
  <h1>London</h1>
  <div>
    <p>With roots at least 7,000 years old, London is an accretion of artifacts old and new, from the remnants of wooden Neolithic settlements buried in the mud of the Thames to gleaming 21st century spires of glass and steel.
    <p>The city is so old that the origins of its very name are unknown: it's first recorded title, <em>Londinium</em>, was provided by the Romans in the first years of the Common Era, but the etymology of the word is completely obscure.
    <p>This extends to some of its architecture: the <em>London Stone</em>, an irregular block of limestone at 111 Cannon Street, has been guarded by an iron grill for centuries, but no-one has known what the stone's purpose is, or why it is there, for the past 1000 years.
  </div>
</main>
!

CSS 

              
                * { box-sizing: border-box; }
body { 
  font-family: Gill Sans;
  margin: 0;
  background: #333;
}
#blurryscroll { 
	top: 0; left: 0; 
  width: 100%;
	height: 5rem;
	overflow: hidden;
	position: fixed;
	filter: blur(4px); 
}
nav { 
	@extend #blurryscroll;
	filter: none; 
  text-align: right;
  
  a { 
    display: inline-block;
    padding: 1rem;
    text-decoration: none;
    color: #000;
    font-size: 1.2rem;
  }
}
main {
  margin: 0;
  background: url(https://s3-us-west-2.amazonaws.com/s.cdpn.io/4273/london_copy.jpg);
  background-size: cover;
  padding: 2rem;
  min-height: 100vh;
  div { 
    margin-top: -6rem;
    width: 40%; 
    margin-left: 30%;
    line-height: 1.3;
    background: rgba(255,255,255,0.75);
    padding: 2rem; 
  }
  h1 { 
    font-weight: 100;
    font-size: 4rem;
  }
  p { font-size: 1.2rem; }
}
@media all and (max-width: 500px) { 
  main div {
    width: 85%;
    margin:  0 auto;
  }
}
!

JS 

              
                var pageContent = document.getElementById("content"),
	pagecopy = pageContent.cloneNode(true),
	blurryContent = document.getElementById("blurryscroll");
	blurryContent.appendChild(pagecopy);
	window.onscroll = function() { blurryContent.scrollTop = window.pageYOffset; }
!
999px

Console