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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.

!
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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About External Resources

You can apply a script from anywhere on the web to your Pen. Just put a URL to it here and we'll add it, in the order you have them, before the JavaScript in the Pen itself.

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

You can also link to another Pen here, and we'll pull the JavaScript from that Pen and include it. If it's using a matching preprocessor, we'll combine the code before preprocessing, so you can use the linked Pen as a true dependency.

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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 class="article-content">

  <h3>Lorem ipsum dolor sit amet.</h3>
  <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Quas temporibus impedit, qui doloribus eos deleniti commodi accusantium vel quibusdam neque ducimus, laudantium tempora iure ullam obcaecati deserunt ipsam pariatur incidunt.</p>
  <h3>Ducimus deserunt amet aliquid laudantium.</h3>
  <p>Eligendi eum neque ipsa voluptate ipsam necessitatibus? Nemo, quis esse voluptatem obcaecati tempore natus? Vel inventore nisi explicabo facilis, autem mollitia earum eos velit quae et adipisci, quos perspiciatis ipsam.</p>
  <h3>Laudantium architecto provident porro sunt.</h3>
  <p>Harum nihil ut dignissimos sed earum, tempore atque praesentium quisquam aperiam cupiditate dolor. Iusto blanditiis neque cupiditate illo perferendis et est vero praesentium enim vitae voluptatem, itaque qui eum obcaecati.</p>

</div>
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CSS 

              
                body {
  max-width: 500px;
  margin: 1rem auto;
  padding: 2rem;
  font: 300 100%/1.6 system-ui;
}

h3 a {
  margin-right: 0.2rem;
}
!

JS 

              
                const $headers = $(".article-content > h3");

$headers.each((i, el) => {
  const $el = $(el);

  // skip it if it already has a link inside
  if ($el.has("a").length != 0) {
    return;
  }

  let idToLink = "";

  // skip it if it already has an id
  if ($el.attr("id") === undefined) {
    // give it ID to match
    idToLink = "article-header-id-" + i;
    $el.attr("id", idToLink);
  } else {
    // make sure the ID matches
    idToLink = $el.attr("id");
  }

  // append a little linky #
  const $headerLink = $("<a />", {
    html: "#",
    class: "article-headline-link",
    href: "#" + idToLink
  });
  $el.addClass("has-header-link").prepend($headerLink);
});
!
999px

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