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HTML

About HTML Preprocessors

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

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).

Add External Stylesheets/Pens

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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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If the script you link to has the file extension of a preprocessor, we'll attempt to process it before applying.

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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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About Packages

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 

              
                progress.c-progress.js-progress(value="0" max="1")

article
    h1 Mobile-friendly reading progress with minimal JS
    each section in [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 ]
        p Lorem ipsum dolor sit amet, consectetur adipiscing elit. Proin porta risus urna, non molestie risus dignissim ut. Maecenas varius leo quis lectus rhoncus mollis. Donec condimentum, ipsum ac consectetur rhoncus, tellus dolor volutpat libero, vitae volutpat mi eros a metus. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Proin at dolor non enim pretium tempor id gravida dui. Pellentesque porta metus in felis molestie gravida. Sed in diam mi. Suspendisse vel odio dapibus, aliquam nisi ut, condimentum ante.

        p In tincidunt dui ac ante efficitur posuere. Integer diam nisl, scelerisque sit amet est non, venenatis suscipit tortor. Integer ultricies bibendum ante et tempus. Donec nibh sem, tempor ac consequat at, rhoncus at elit. Fusce aliquam tempus ex, vitae venenatis ipsum mattis aliquet. Aliquam convallis lacinia lectus, sit amet consectetur augue aliquam eu. Morbi enim mi, scelerisque non viverra in, mattis vitae ligula. Donec nulla lacus, interdum ac tortor vitae, consectetur sodales lorem. Morbi iaculis ante sit amet lacus maximus, non elementum libero scelerisque. Vivamus id magna convallis, ullamcorper nisl eu, efficitur ipsum. Praesent eros ante, maximus et quam vitae, laoreet blandit neque.
!

CSS 

              
                $progress-color: lighten(#1e1935, 20)

.c-progress
    position: fixed
    top: 0
    left: 0
    width: 100%
    height: 5px
    appearance: none
    background: transparent
    border: none
    color: $progress-color
    z-index: 5

    &::-webkit-progress-bar
        background: transparent

    &::-webkit-progress-value
        background: $progress-color

    &::-moz-progress-bar
        background: $progress-color

    
article
    margin: 0 auto
    width: 65%
    max-width: 700px
    
p
    font: 16px/#{1.5} "Poppins", Arial, sans-serif
    margin-bottom: 2em

h1
    font: bold 46px/#{1.25} "Poppins", Arial, sans-serif
    margin: 1.5em 0

*
    -webkit-font-smoothing: antialisased
    box-sizing: border-box
!

JS 

              
                //- Reading Progress Indicator

{
    const progress = document.querySelector('.js-progress');
    const body = document.body;
    const html = document.documentElement;

    const updateSizes = () => ({
        height: Math.max(body.scrollHeight, body.offsetHeight, html.clientHeight, html.scrollHeight, html.offsetHeight),
        vh: Math.max(html.clientHeight, window.innerHeight || 0)
    });

    let scrollY = 0;
    let sizes = updateSizes();

    const update = () => progress.setAttribute('value', 100 - (sizes.height - scrollY - sizes.vh) / sizes.height * 100);

    const onScroll = () => {
        scrollY = (window.pageYOffset || document.scrollTop) - (document.clientTop || 0);
        requestAnimationFrame(update);
    }

    const onResize = () => {
        sizes = updateSizes();
        requestAnimationFrame(update);
    }

    if(progress) {
        progress.setAttribute('max', 100);
        window.addEventListener('scroll', onScroll, false);
        window.addEventListener('resize', onResize, false);
    }
}
!
999px

Console