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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 URL's added here will be added as <link>s in order, and before the CSS in the editor. If you link to another Pen, it will include the CSS from that Pen. If the preprocessor matches, it will attempt to combine them before processing.

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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.

If the stylesheet 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 CSS 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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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 Skypack, which makes packages from npm not only available on a CDN, but prepares them for native JavaScript ES6 import 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

Save Automatically?

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Auto-Updating Preview

If enabled, the preview panel updates automatically as you code. If disabled, use the "Run" button to update.

Format on Save

If enabled, your code will be formatted when you actively save your Pen. Note: your code becomes un-folded during formatting.

Editor Settings

Code Indentation

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Visit your global Editor Settings.

HTML 

              
                <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Quidem deleniti accusantium quasi ab ad officia cupiditate sed aliquam nobis expedita velit dolorum perspiciatis pariatur nam vero et magnam soluta tempora!</p>
<p>Eveniet deserunt consequatur porro molestiae nulla optio quis totam libero iste nemo odit eum facilis sapiente. Harum similique cupiditate voluptas ea optio sunt molestias eius ab qui obcaecati nesciunt id?</p>
<p>Necessitatibus delectus sint vitae eos quasi optio esse dignissimos enim laborum ipsum harum perspiciatis eaque. Magnam fugiat delectus neque laboriosam in accusamus a veniam inventore asperiores consequatur nihil quae quo.</p>
<p>Eligendi quaerat nesciunt sint nobis qui? Temporibus maiores esse molestiae hic cum culpa sed recusandae dolore sequi modi. Quos illum debitis odio consequatur voluptatum error aliquam rem similique officia recusandae.</p>
<p>Ex suscipit earum reiciendis eaque dolorem inventore accusantium modi voluptatum saepe cum quam tempora autem corrupti illum deleniti iure rerum mollitia quo ducimus soluta ea! Illum aliquid consectetur vitae quod?</p>
<p>Minus rem tempora quo. Deleniti mollitia dignissimos laborum quis quos facilis dolore soluta error provident recusandae veniam minus consequatur blanditiis. Facere tempore praesentium soluta fugiat quia eligendi dolores ullam doloribus!</p>
<p>Aut nulla perferendis officiis accusamus ut aspernatur hic possimus amet blanditiis incidunt repudiandae ullam inventore ipsam recusandae nihil provident facilis totam quibusdam natus eligendi optio quia sapiente rerum quos illo?</p>
<p>Porro soluta nisi impedit voluptatem ex accusantium facilis amet quod blanditiis quia similique totam enim id ratione minus quo modi sequi nam dicta iste aliquid itaque velit accusamus quibusdam consequuntur.</p>
<p>Ab assumenda in ad nesciunt recusandae labore voluptates vero suscipit tenetur ullam sint beatae odio harum quo aperiam quas temporibus pariatur consectetur saepe eveniet minus voluptatem atque iusto similique repudiandae?</p>
<p>In enim odit repellat maxime harum eum expedita fuga vel eaque quaerat optio hic sapiente eveniet neque dolorum eligendi pariatur possimus aliquid minus officiis mollitia quia voluptates sunt nulla est!</p>
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CSS 

              
                body::-webkit-scrollbar {
  width: 2em;
}
body::-webkit-scrollbar-track {
  box-shadow: inset 0 0 6px rgba(0, 0, 0, 0.3);
}
body::-webkit-scrollbar-thumb {
  background: linear-gradient(45deg, orange, darksalmon);
}

html {
  background: lightgrey;
  height: 100%;
  overflow: hidden;
}
body {
  height: 100%;
  background: whitesmoke;
  overflow-y: scroll;
  max-width: 300px;
  margin: 0 auto;
  padding: 3em;
  font: 100%/1.4 serif;
  border: 1px solid rgba(0, 0, 0, 0.25);
}
p {
  margin: 0 0 1.5em;
}
* {
  box-sizing: border-box;
}
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JS
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999px

Console