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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

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 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.

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Code Indentation

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Visit your global Editor Settings.

HTML 

              
                <nav class='fixed'>
  <ul>
    <li><a href="#">Item1</a></li>
    <li><a href="#">Item1</a></li>
    <li><a href="#">Item1</a></li>
    <li><a href="#">Item1</a></li>
  </ul>
</nav>
<div class='header'>
  <div class='banner'></div>
  <nav>
    <ul>
      <li><a href="#">Item1</a></li>
      <li><a href="#">Item1</a></li>
      <li><a href="#">Item1</a></li>
      <li><a href="#">Item1</a></li>
    </ul>
  </nav>
</div>
<div class='body'>
  <p>
    Lorem ipsum dolor sit amet, consectetur adipiscing elit. Etiam vestibulum ex eget erat consectetur, ut vestibulum enim consectetur. Fusce urna lectus, egestas vitae dolor at, ultricies cursus neque. Duis elementum iaculis purus. Sed dictum tincidunt tortor
    quis fermentum. Vestibulum tincidunt purus erat, vel pellentesque massa tempor ut. In risus est, rutrum vitae auctor a, suscipit pharetra tortor. Quisque sit amet ornare purus. Sed sit amet pellentesque enim, sit amet molestie ipsum. Nullam at vestibulum
    lorem, quis laoreet nulla. Curabitur semper, turpis vel placerat faucibus, magna ex rutrum lorem, nec lobortis diam ex eu nibh. Cras fermentum magna leo, at porttitor arcu consequat vel. Nam lobortis magna ac tempor malesuada. Donec ultrices, mauris
    a molestie accumsan, elit est pharetra felis, quis semper elit magna eleifend turpis. Etiam pellentesque elit sit amet augue egestas porta nec sit amet nibh.
  </p>
  <p>
    Nullam dictum nulla ac nisl finibus venenatis. Aliquam eget tincidunt ex. Cum sociis natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Proin eu lorem imperdiet, feugiat ex eu, facilisis sapien. Ut vulputate nisi nisi, eget rutrum
    magna fringilla ut. In hac habitasse platea dictumst. Aenean ut quam sodales, congue mauris eu, pellentesque ligula. Quisque pulvinar eget velit non interdum. Donec imperdiet augue posuere ligula aliquam porta vel a turpis. Donec sit amet fermentum
    purus. Phasellus lacinia nunc urna, id gravida eros consequat a.
  </p>
  <p>
    In scelerisque lacus in metus auctor, nec congue massa facilisis. Sed ut egestas metus. Mauris vel justo nulla. Mauris neque nulla, venenatis et nibh sed, interdum vestibulum ligula. Curabitur id felis ac nunc porttitor sagittis nec eget massa. Donec
    volutpat libero ut purus condimentum, a iaculis dui elementum. Sed felis purus, molestie nec dui sed, pharetra congue felis. Proin a imperdiet nulla, in porta tellus.
  </p>
  <p>
    Fusce interdum est dolor, vel suscipit lorem lobortis at. Nam nec maximus elit. Aliquam in fermentum dui, quis fringilla tortor. Cum sociis natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. In auctor sed dui non venenatis. Donec
    interdum hendrerit mi, id mollis justo tincidunt sed. Morbi et mauris aliquam, imperdiet erat eget, condimentum orci. In tristique at turpis vitae lobortis. In vel ullamcorper sapien. Morbi venenatis lorem velit, non tempus mi feugiat quis. Morbi
    vel condimentum urna. Praesent quam turpis, congue nec elit nec, vulputate dictum mi.
  </p>
  <p>
    Pellentesque posuere finibus justo, in volutpat felis euismod ac. Suspendisse vestibulum porta lectus pulvinar sagittis. Ut lobortis venenatis ante, ac semper nisl cursus quis. Ut at malesuada magna, id aliquam lectus. Ut ac nisl at ante volutpat consectetur
    bibendum at sapien. Vestibulum quis luctus lectus. Duis at aliquet risus, non dapibus odio. Aenean ac tortor ligula. Praesent finibus lectus id dignissim condimentum. Morbi magna ipsum, consequat vel aliquet vel, fringilla quis est.
  </p>
</div>
!

CSS 

              
                html,
body {
  margin: 0;
}

nav {
  background: #ddd;
}

nav ul {
  width: 80%;
  margin: 0 auto;
  padding: 0;
  list-style: none;
}

nav ul li {
  display: inline-block;
}

nav ul li a {
  display: inline-block;
  padding: 0 20px;
  line-height: 40px;
  text-decoration: none;
}

nav ul li a:hover {
  background: #ccc;
}

nav.fixed {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
}

.header {
  position: relative;
}

.banner {
  height: 300px;
  background: #990000;
}

.body {
  height: 1000px;
  width: 80%;
  margin: 0 auto;
}
!

JS 

              
                /*
  No JS
*/
!
999px

Console