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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

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.

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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-.

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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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 

              
                <div>
    <h1>CSSOM Example</h1>

    <p>Using the CSS object model exposed by CSS Regions you can create regions dynamically at runtime.</p>
    <article id="art">
        <div class="myregions region-small-height"></div>
        <div class="myregions region-small-height"></div>
    </article>
</div>
<div id="source">
    <p>
        CSS Pseudo-elements is a new proposal by Adobe to the W3C that allows multiple "before" and "after" pseudo-elements to be generated by a single element.
        In this example you can see how another region (the blue one) is added after the page is loaded and the CSSRegions object is created.
        <a href="http://corlan.org">This is a very long link!</a>
    </p>
    <p>
        Multiple pseudo-elements cover use cases collected on css-tricks.com.
    </p>
    <p>
        This is a prototype JavaScript implementation to give you a feel for how the code will look like and behave. Please keep in mind that this is just experimental stuff and treat it accordingly.
    </p>
</div>
!

CSS 

              
                      body {
            width: 80%;
            margin: 50px 10% 10%;
            font-family: Palatino, Georgia, serif;
            background-color: white;
        }

        #source {
            flow-into: article;
            clear: both;
        }

        .myregions {
            flow-from: article;
            region-fragment: break;
            float: left;
            width: 25%;
            min-width: 200px;
            margin: 0px 20px 20px;
            padding: 7px;
            background-color: #b0dcff;
            height: auto;
        }

        .region-small-height {
            background-color: #dedede;
            height: 200px;
            overflow: hidden;
        }

        p {
            line-height: 1.6em;
            margin-top: 0px;
        }
!

JS 

              
                   function init(){
        
        function on_region_update(e) {
            var art, div;
            if (e.target.overset) {
                div = document.createElement("div");
                div.className = "myregions";
                art = document.getElementById("art");
                art.appendChild(div);
            }
        }
        
        var flow = document.getNamedFlow("article");
        flow.addEventListener("regionfragmentchange", on_region_update);
        on_region_update({target:flow});
        
    }
    
    window.addEventListener('load', init)
!
999px

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