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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

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.

!
Insecure Resource

The resource you are linking to is using the 'http' protocol, which may not work when the browser is using https.

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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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.

All packages are different, so refer to their docs for how they work.

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HTML 

              
                    <div id="root"></div>
<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Aenean finibus dui nec diam sagittis suscipit. Vestibulum vitae purus id dui interdum consequat. Donec convallis, libero et pretium luctus, est diam dapibus sapien, in posuere diam ante ut risus. Fusce tortor lorem, ornare vel risus nec, finibus rutrum mauris. Quisque elementum lorem massa, vel convallis ex pretium eget. Suspendisse tempus elementum erat vitae dapibus. Integer elementum mauris in dui tristique eleifend. Vivamus quis volutpat erat, vitae interdum ipsum. Aliquam erat volutpat. Etiam eu mauris eget neque commodo ultricies. Donec vel tellus augue.</p>

<p>Curabitur malesuada fermentum vestibulum. Quisque accumsan gravida dignissim. Quisque vel suscipit felis, non porttitor nulla. In gravida tellus lorem. Nam tincidunt lacinia finibus. Sed non metus dapibus, pharetra leo non, blandit dui. Fusce nec pharetra massa. Proin varius, est in finibus lacinia, libero lectus dictum dolor, sodales tempus nulla libero non nisl. Phasellus ut orci arcu. Praesent pellentesque nec dolor eget consectetur. Curabitur pulvinar vitae mi sit amet aliquet. Sed mauris risus, pellentesque at consequat ac, placerat at quam. Phasellus sed elementum tellus, eget interdum libero. Fusce sollicitudin nisi molestie augue feugiat tempus.</p><p>

Maecenas hendrerit arcu et porta cursus. Aliquam erat volutpat. Suspendisse in malesuada orci, nec porta elit. Mauris ac ultricies lectus. Quisque pulvinar sapien viverra nisl ultricies convallis feugiat ut eros. Fusce sed mauris sit amet sem tincidunt convallis. Aliquam quis eleifend neque.</p>
<p>
Duis volutpat dignissim luctus. Nullam justo arcu, dictum vel dictum non, blandit non metus. Sed vehicula, dui non elementum ultrices, mauris ipsum varius mauris, sed sagittis felis augue nec ante. Nunc ante erat, venenatis sit amet mauris et, venenatis consectetur nulla. Nunc elementum venenatis hendrerit. Orci varius natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Fusce finibus lacus sed lacinia laoreet. Donec eu lectus augue. Fusce nec elit eu eros sodales finibus. In imperdiet feugiat eleifend. Donec molestie libero ac ex vestibulum fermentum. Vivamus ultrices orci quis risus tristique, et vulputate dui posuere.</p>
<p>
Sed id tincidunt justo. Etiam at odio condimentum, blandit tortor sit amet, bibendum est. Sed mi erat, tincidunt ut nisl id, pharetra bibendum ipsum. Maecenas tristique ultrices turpis eget tincidunt. In tempor quam quis magna hendrerit, in accumsan augue semper. Aenean facilisis, mauris eget pharetra tempor, lorem justo ullamcorper nulla, et tempus dolor arcu ac risus. Vivamus quam ante, congue ut sodales et, maximus in dolor. Suspendisse accumsan enim et risus scelerisque, in tincidunt eros ullamcorper. Integer commodo imperdiet lacus, non semper erat viverra eget. Maecenas lobortis lobortis velit vehicula convallis. Donec porta tincidunt dolor, at maximus nulla consectetur eu.</p>
<p>
Sed id tincidunt justo. Etiam at odio condimentum, blandit tortor sit amet, bibendum est. Sed mi erat, tincidunt ut nisl id, pharetra bibendum ipsum. Maecenas tristique ultrices turpis eget tincidunt. In tempor quam quis magna hendrerit, in accumsan augue semper. Aenean facilisis, mauris eget pharetra tempor, lorem justo ullamcorper nulla, et tempus dolor arcu ac risus. Vivamus quam ante, congue ut sodales et, maximus in dolor. Suspendisse accumsan enim et risus scelerisque, in tincidunt eros ullamcorper. Integer commodo imperdiet lacus, non semper erat viverra eget. Maecenas lobortis lobortis velit vehicula convallis. Donec porta tincidunt dolor, at maximus nulla consectetur eu.</p>
<p>
Sed id tincidunt justo. Etiam at odio condimentum, blandit tortor sit amet, bibendum est. Sed mi erat, tincidunt ut nisl id, pharetra bibendum ipsum. Maecenas tristique ultrices turpis eget tincidunt. In tempor quam quis magna hendrerit, in accumsan augue semper. Aenean facilisis, mauris eget pharetra tempor, lorem justo ullamcorper nulla, et tempus dolor arcu ac risus. Vivamus quam ante, congue ut sodales et, maximus in dolor. Suspendisse accumsan enim et risus scelerisque, in tincidunt eros ullamcorper. Integer commodo 
  <p>imperdiet lacus, non semper erat viverra eget. Maecenas lobortis lobortis velit vehicula convallis. Donec porta tincidunt dolor, at maximus nulla consectetur eu.</p>
Sed id tincidunt justo. Etiam at odio condimentum, blandit tortor sit amet, bibendum est. Sed mi erat, tincidunt ut nisl id, pharetra bibendum ipsum. Maecenas tristique ultrices turpis eget tincidunt. In tempor quam quis magna hendrerit, in accumsan augue semper. Aenean facilisis, mauris eget pharetra tempor, lorem justo ullamcorper nulla, et tempus dolor arcu ac risus. Vivamus quam ante, congue ut sodales et, maximus in dolor. Suspendisse accumsan enim et risus scelerisque, in tincidunt eros ullamcorper. Integer commodo imperdiet lacus, non semper erat viverra eget. Maecenas lobortis lobortis velit vehicula convallis. Donec porta tincidunt dolor, at maximus nulla consectetur eu.</p>
!

CSS 

              
                body{
  margin:0;
    font-family: sans-serif;
}
.scroller{
  position:fixed;
  font-size:2rem;
  bottom:1em;
  right:1em;
}
.progress{
  position:fixed;
  top:0;
  height:1em;
}
button{
   display: inline-block;
    border: none;
    padding: 1rem 1rem;
    margin: 0;
    background:inherit;
    text-decoration: none;
    font-size: 1rem;
    line-height: 1;
    cursor: pointer;
}
.percent{
  display: inline-block;
    font-size: 1rem;
  text-align:center;
    line-height: 1;
    padding: 1rem 1rem;
}
!

JS 

              
                import React from 'https://cdn.skypack.dev/react';
import ReactDOM from 'https://cdn.skypack.dev/react-dom';

const {useState,useEffect} = React; 

function Scroller(){
  const [scrollPosition, setScrollPosition] = useState(window.scrollY);
  const [color,setColor] = useState({r:200,g:100,b:100});
 
  useEffect(()=>{
   document.addEventListener("scroll",handleScroll);
    return ()=>{document.removeEventListener("scroll",handleScroll);}
  },[]);
  
  function onColorChange(){
    const newColor = {r:100+Math.random()*155,g:100+Math.random()*155,b:100+Math.random()*155};
    setColor(newColor);
  }

  function handleScroll(e){
    const scrollDistance = document.body.scrollTop || document.documentElement.scrollTop;
    const documentHeight = document.documentElement.scrollHeight - document.documentElement.clientHeight;
    const percentAlong =  (scrollDistance / documentHeight);
    setScrollPosition(percentAlong);
  }
  
  return <>
    <div class="progress" id="progress"
   style={{backgroundColor:`rgba(${color.r},${color.g},${color.b},${scrollPosition})`,width: `${scrollPosition*100}%`}}></div>
    <div className="scroller" style={{backgroundColor:`rgb(${color.r},${color.g},${color.b})`}}>
    <button onClick={onColorChange}>Change color</button>
    <span class="percent">{Math.round(scrollPosition * 100)}%</span>
  </div>
  </>
}

ReactDOM.render(<Scroller/>,document.getElementById("root"))
!
999px

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