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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

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

Any URLs added here will be added as <link>s in order, and before the CSS in the editor. You can use the CSS from another Pen by using its URL and the proper URL extension.

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About External Resources

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

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

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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.

Add External Scripts/Pens

Any URL's added here will be added as <script>s in order, and run before the JavaScript in the editor. You can use the URL of any other Pen and it will include the JavaScript from that Pen.

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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.

If you're using React / ReactDOM, make sure to turn on Babel for the JSX processing.

Behavior

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HTML 

              
                <p class="one">Lorem ipsum dolor sit amet consectetur adipisicing elit. Hic assumenda rem harum dicta beatae incidunt ducimus ullam, neque quos sapiente obcaecati id reprehenderit officia quas ea eum quod error architecto. Lorem ipsum dolor sit amet consectetur, adipisicing elit. Assumenda eveniet quis optio at laborum autem voluptate, voluptas ratione rerum amet perferendis nihil! Consectetur quisquam rerum iusto dolores animi nam explicabo.</p>

<p class="two">Lorem ipsum dolor sit amet consectetur adipisicing elit. Ratione tempore quibusdam assumenda omnis aspernatur, incidunt voluptatem? Fuga recusandae sunt, qui voluptatem nihil laboriosam, odit eligendi incidunt pariatur ut veritatis sed voluptates itaque rerum fugit rem eveniet. Natus optio libero est suscipit id quas accusamus repellat provident. Iure cupiditate libero nihil at sint, ex repellat labore dolorum consequatur magnam vitae ratione cumque. Totam magnam repellendus, possimus quasi, omnis facilis dolorum cupiditate non vitae, deserunt quas doloribus? Accusamus quasi unde consequatur vel illo soluta ab laborum non nihil. Natus, iusto architecto nesciunt dolor laboriosam magni eaque vitae in suscipit quo ad alias!</p>

<p class="three">Lorem ipsum dolor sit, amet consectetur adipisicing elit. Possimus quo nemo impedit? Ducimus dolores, excepturi, qui quis, officiis dolorem consequuntur libero nam temporibus distinctio facere ex totam quidem sit autem? Doloribus dolor ducimus dolorem autem fugiat eos itaque. Commodi amet perferendis quaerat earum minus ea modi rem. Beatae soluta explicabo est provident dolor atque dignissimos? Eius, eaque? Culpa laborum voluptate neque nobis eligendi consequuntur suscipit dolor aperiam, eius molestiae praesentium quaerat aut eum recusandae tenetur porro iusto, debitis itaque maxime! Aperiam reprehenderit veritatis ducimus ad, autem omnis aspernatur a odio hic magnam ea voluptatibus quos pariatur dignissimos exercitationem esse qui facilis reiciendis suscipit praesentium. Repudiandae, blanditiis voluptatum. Aliquam esse, sit accusantium commodi cumque officiis quod perspiciatis, ullam consectetur deserunt vel!</p>

<p class="four">Lorem ipsum dolor sit amet consectetur adipisicing elit. Quidem autem, nobis fugit dolore vitae illo neque iure cupiditate aspernatur sunt nihil, obcaecati corporis expedita recusandae. Consectetur eveniet quae suscipit dolore est corporis asperiores maxime non sunt, excepturi unde adipisci iure? Necessitatibus, sunt maiores. Cumque, porro ad harum deserunt possimus suscipit voluptas ducimus perspiciatis facilis, molestiae, distinctio eaque libero earum unde consequuntur expedita? Fugiat magni rerum delectus ut, error numquam quaerat asperiores adipisci corporis deserunt praesentium sint debitis quae perspiciatis aliquid.</p>

<p class="five">Lorem ipsum dolor sit amet consectetur adipisicing elit. Provident minima nihil, eum sapiente ex neque asperiores delectus amet, ea dolorum nulla quod vitae, maiores nisi? Voluptatum aspernatur quas vero quod libero laborum maxime? Sapiente consectetur dolore odio, amet, tempora suscipit accusamus quisquam reiciendis voluptates recusandae minus vero reprehenderit, ea perspiciatis commodi iusto laborum laboriosam. Repudiandae, maxime! Nesciunt in molestias odio quae, voluptatem perferendis, laudantium nobis voluptates repellendus ad ipsa nisi.</p>
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CSS 

              
                .one::selection {
  color: skyblue;
  background-color: #000;
}

.two::selection {
  color: #fff;
}

.three::selection {
  text-shadow: 2px 2px 2px #ff3;
  color: #333;
}

.four::selection {
  text-shadow: 2px 2px 1px #000;
  color: #fff;
  background: red;
}
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JS
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999px

Console