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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

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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.

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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="content">
  <p>Content goes here</p>
  <br />
  <button id="toggle">Toggle Copy</button>
</div>
<footer>
	I'm a sticky footer
</footer>
!

CSS 

              
                * {
  margin: 0;
  padding: 0;
  font-family: Roboto,"Helvetica Neue",Arial,sans-serif;
}
body {
  display: flex;
  flex-direction: column;
  min-height: 100vh;
  color: #fff;
}
.content {
  background: #FFD166;
  flex: 1 0 auto;
  padding: 2rem;
  width: 50%;
  margin: 0 auto;
}
footer {
  background: #EF476F;
  padding: 2rem;
}
button {
  padding: 1rem;
}
!

JS 

              
                const button = document.getElementById("toggle");
const content = document.querySelector("p");
let toggled = false;
button.addEventListener("click", function() {
  toggled = !toggled;
  console.log(toggled);
    if (toggled) {
    content.innerHTML = "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Duis tincidunt lacus ut turpis blandit, vel dictum augue suscipit. Curabitur dolor lorem, posuere eget maximus ut, laoreet at felis. Duis tempor, metus et pellentesque dignissim, turpis nisi luctus ipsum, ut tempor urna nisi sed nisi. Fusce non lacus non quam lacinia ultrices. Curabitur lorem nisi, sollicitudin nec odio non, congue convallis libero. Aliquam erat volutpat. Donec non quam pellentesque, feugiat elit ut, ornare velit. Etiam feugiat velit at lorem volutpat, sed consectetur odio efficitur. Fusce ut erat velit. Nullam mauris purus, congue ac libero et, condimentum auctor lectus. Nulla ultricies porta scelerisque.<br />Vivamus dictum nec odio sit amet viverra. Donec pharetra ornare ex, eget posuere ex bibendum suscipit. Sed non nunc ac mauris mattis ullamcorper id sed elit. Vivamus ultrices luctus ante et tempor. Sed efficitur tellus vitae metus mattis, eget eleifend dolor viverra. Morbi sit amet nisi eros. Praesent dignissim massa eu risus tincidunt, ut tempus purus sollicitudin.<br />Donec eget metus auctor, lobortis libero a, accumsan neque. Morbi sit amet dignissim urna. Interdum et malesuada fames ac ante ipsum primis in faucibus. Sed at augue rhoncus, sollicitudin odio quis, malesuada purus. Fusce pretium lorem id tellus tempus, id commodo erat tincidunt. Ut facilisis elit sodales mauris vulputate, quis vulputate massa viverra. Donec quis eros erat. Sed ornare elit eget lectus vestibulum fringilla. Curabitur condimentum pharetra bibendum. Donec rutrum dui sem, nec luctus nisi maximus vitae.<br />Aenean venenatis massa tempus gravida dictum. Donec pellentesque vestibulum est non consectetur. Nulla justo ex, ultricies in eleifend non, rhoncus at leo. Etiam consectetur est quis malesuada maximus. Mauris sed nulla in justo varius euismod. Nulla elementum elementum rhoncus. Nam tempor, erat nec dignissim tincidunt, arcu magna vestibulum tortor, ac vestibulum ligula dui ut sapien. Proin in odio rutrum, volutpat ligula sed, feugiat est. Morbi tempor finibus erat, ac venenatis turpis volutpat at. Vivamus vitae libero sit amet nisl tristique rutrum. In condimentum laoreet quam, eu imperdiet enim placerat et. Fusce a tellus interdum, varius turpis eu, volutpat nunc.<br />Pellentesque lobortis posuere quam, in luctus est. Donec venenatis neque sit amet dui mollis, a ornare nisl tristique. Fusce urna enim, semper non lacinia ut, hendrerit scelerisque neque. Etiam dolor nunc, sodales ut suscipit sed, egestas eu odio. Duis feugiat tempus leo ut tincidunt. Morbi augue neque, fringilla vitae tellus sit amet, rutrum tincidunt lacus. Class aptent taciti sociosqu ad litora torquent per conubia nostra, per inceptos himenaeos. Proin volutpat blandit enim, in faucibus tellus placerat sit amet. Nullam rhoncus molestie mauris nec pellentesque. Donec eget elit ut nisl sollicitudin tempor vitae et purus.<br />Lorem ipsum dolor sit amet, consectetur adipiscing elit. Duis tincidunt lacus ut turpis blandit, vel dictum augue suscipit. Curabitur dolor lorem, posuere eget maximus ut, laoreet at felis. Duis tempor, metus et pellentesque dignissim, turpis nisi luctus ipsum, ut tempor urna nisi sed nisi. Fusce non lacus non quam lacinia ultrices. Curabitur lorem nisi, sollicitudin nec odio non, congue convallis libero. Aliquam erat volutpat. Donec non quam pellentesque, feugiat elit ut, ornare velit. Etiam feugiat velit at lorem volutpat, sed consectetur odio efficitur. Fusce ut erat velit. Nullam mauris purus, congue ac libero et, condimentum auctor lectus. Nulla ultricies porta scelerisque.<br />Vivamus dictum nec odio sit amet viverra. Donec pharetra ornare ex, eget posuere ex bibendum suscipit. Sed non nunc ac mauris mattis ullamcorper id sed elit. Vivamus ultrices luctus ante et tempor. Sed efficitur tellus vitae metus mattis, eget eleifend dolor viverra. Morbi sit amet nisi eros. Praesent dignissim massa eu risus tincidunt, ut tempus purus sollicitudin.<br />Donec eget metus auctor, lobortis libero a, accumsan neque. Morbi sit amet dignissim urna. Interdum et malesuada fames ac ante ipsum primis in faucibus. Sed at augue rhoncus, sollicitudin odio quis, malesuada purus. Fusce pretium lorem id tellus tempus, id commodo erat tincidunt. Ut facilisis elit sodales mauris vulputate, quis vulputate massa viverra. Donec quis eros erat. Sed ornare elit eget lectus vestibulum fringilla. Curabitur condimentum pharetra bibendum. Donec rutrum dui sem, nec luctus nisi maximus vitae.<br />Aenean venenatis massa tempus gravida dictum. Donec pellentesque vestibulum est non consectetur. Nulla justo ex, ultricies in eleifend non, rhoncus at leo. Etiam consectetur est quis malesuada maximus. Mauris sed nulla in justo varius euismod. Nulla elementum elementum rhoncus. Nam tempor, erat nec dignissim tincidunt, arcu magna vestibulum tortor, ac vestibulum ligula dui ut sapien. Proin in odio rutrum, volutpat ligula sed, feugiat est. Morbi tempor finibus erat, ac venenatis turpis volutpat at. Vivamus vitae libero sit amet nisl tristique rutrum. In condimentum laoreet quam, eu imperdiet enim placerat et. Fusce a tellus interdum, varius turpis eu, volutpat nunc.<br />Pellentesque lobortis posuere quam, in luctus est. Donec venenatis neque sit amet dui mollis, a ornare nisl tristique. Fusce urna enim, semper non lacinia ut, hendrerit scelerisque neque. Etiam dolor nunc, sodales ut suscipit sed, egestas eu odio. Duis feugiat tempus leo ut tincidunt. Morbi augue neque, fringilla vitae tellus sit amet, rutrum tincidunt lacus. Class aptent taciti sociosqu ad litora torquent per conubia nostra, per inceptos himenaeos. Proin volutpat blandit enim, in faucibus tellus placerat sit amet. Nullam rhoncus molestie mauris nec pellentesque. Donec eget elit ut nisl sollicitudin tempor vitae et purus.";
  } else {
    content.innerHTML = "Content goes here";
  }
});
!
999px

Console