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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).

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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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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>
  <p>Lorem ipsum, dolor sit amet consectetur adipisicing elit. Sapiente facilis aperiam saepe modi quis totam sed reiciendis eaque sit adipisci. Voluptatem, perferendis distinctio quos quod dolorum error quisquam recusandae libero.</p>
  <p>Velit commodi sapiente laudantium eos porro dolorum ipsam similique explicabo soluta nemo facere obcaecati quibusdam, praesentium incidunt architecto voluptate nobis. Praesentium placeat, ex suscipit at eaque autem distinctio sed rerum!</p>
  <p>Omnis corporis incidunt accusamus ut. Facere corrupti eaque, similique repudiandae quos odit dignissimos voluptatum vero reprehenderit! Nam ducimus quia ut, perferendis numquam consequatur veritatis sit voluptates eos molestias assumenda reprehenderit!</p>
  <p>Eius esse laudantium dolores, vero ad culpa modi veritatis aut dolore unde fugit quisquam excepturi exercitationem ratione ex quidem rem et doloremque! Odio magnam assumenda repudiandae. Magnam nobis veritatis nostrum.</p>
  <p>Est ipsum inventore dolores perferendis accusamus expedita pariatur, necessitatibus cum eaque, sapiente alias possimus! Vero, tempore aliquid ducimus dolore laboriosam accusantium illo hic unde sit in quod iste eum totam.</p>
  <p>Asperiores beatae sapiente repellat! Ullam neque non fuga tempora ratione excepturi beatae in consequatur, perferendis illo nam earum voluptas maiores? Assumenda molestiae veritatis maxime obcaecati enim? Odio cum itaque porro!</p>
  <p>Culpa cumque eos nam nesciunt eaque! Blanditiis, necessitatibus repellat quo ad quia quos cum sapiente consequuntur? Possimus distinctio id enim porro soluta quae neque, eveniet, cum consequatur nulla facere similique?</p>
  <p>Ipsa, placeat ab. Eius temporibus consectetur, earum omnis quia deserunt ducimus illum. Omnis eius voluptate veniam praesentium minus quibusdam, ab ducimus, voluptatem in totam odit quos nihil sed! Molestiae, quisquam!</p>
  <p>Eius animi adipisci debitis excepturi molestiae dolorem incidunt dolores commodi sint laboriosam. Non, ad! Quidem assumenda, earum, reiciendis molestiae a hic in sunt nesciunt nostrum fugit praesentium debitis eius labore.</p>
  <p>Quisquam, cumque vitae sit unde beatae delectus nam atque odit alias temporibus dolorum eaque sint mollitia dignissimos! Maxime maiores nulla unde consequuntur excepturi rem. Iste dolore fugit voluptatibus earum delectus.</p>
</div>
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CSS 

              
                p:nth-child(6n + 1)::selection {
  background: hsl(0deg, 100%, 77%);
  color: hsl(0deg, 100%, 16%);
}
p:nth-child(6n + 2)::selection {
  background: hsl(33deg, 100%, 79%);
  color: hsl(33deg, 100%, 18%);
}
p:nth-child(6n + 3)::selection {
  background: hsl(56deg, 100%, 79%);
  color: hsl(56deg, 100%, 18%);
}
p:nth-child(6n + 4)::selection {
  background: hsl(120deg, 78%, 90%);
  color: hsl(120deg, 78%, 29%);
}
p:nth-child(6n + 5)::selection {
  background: hsl(217deg, 100%, 90%);
  color: hsl(217deg, 100%, 29%);
}
p:nth-child(6n + 6)::selection {
  background: hsl(261deg, 78%, 66%);
  color: hsl(261deg, 78%, 5%);
}

p {
  max-width: 700px;
  font-size: 18px;
  text-align: center;
  margin: 0 auto;
  padding: 10px 0; 
  font-family: cursive;
}
!

JS
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999px

Console