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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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+ add another resource

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.

Learn more

+ add another resource

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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Format on Save

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

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Visit your global Editor Settings.

HTML 

              
                <body>
  <h1>"Copy bookmark link to clipboard" button</h1>
  <p>
    Lorem ipsum dolor sit amet, consectetur adipisicing elit. Iure veritatis
    expedita id. Reprehenderit cum in exercitationem tempore, a rem
    praesentium iusto nam ducimus tempora totam minus, fuga, reiciendis
    necessitatibus quisquam!
  </p>
  <p>
    Lorem ipsum dolor sit amet consectetur adipisicing elit. Accusantium quis,
    alias inventore distinctio laboriosam, quisquam nemo excepturi ipsum
    necessitatibus quia, iusto illum cupiditate eius corporis labore provident
    dignissimos? Iste, dignissimos.
  </p>
  <p>
    Lorem ipsum dolor sit amet consectetur adipisicing elit. Accusantium quis,
    alias inventore distinctio laboriosam, quisquam nemo excepturi ipsum
    necessitatibus quia, iusto illum cupiditate eius corporis labore provident
    dignissimos? Iste, dignissimos.
  </p>
  <h2>First heading 2</h2>
  <p>
    Lorem ipsum dolor sit amet consectetur adipisicing elit. Nihil fugit,
    distinctio ex incidunt sint sed unde, perferendis, quos modi nulla dolore
    cumque delectus doloremque ab repudiandae earum nemo in adipisci.
  </p>
  <p>
    Lorem ipsum dolor sit amet consectetur adipisicing elit. Accusantium quis,
    alias inventore distinctio laboriosam, quisquam nemo excepturi ipsum
    necessitatibus quia, iusto illum cupiditate eius corporis labore provident
    dignissimos? Iste, dignissimos.
  </p>
  <p>
    Lorem ipsum dolor sit amet consectetur adipisicing elit. Accusantium quis,
    alias inventore distinctio laboriosam, quisquam nemo excepturi ipsum
    necessitatibus quia, iusto illum cupiditate eius corporis labore provident
    dignissimos? Iste, dignissimos.
  </p>
  <h3>A heading 3</h3>
  <p>
    Lorem ipsum dolor sit amet consectetur adipisicing elit. Voluptates harum
    ipsum, expedita et reprehenderit error asperiores repudiandae aspernatur
    eum optio. Illo unde odit, inventore praesentium et quia voluptatum
    cupiditate similique?
  </p>
  <p>
    Lorem ipsum dolor sit amet consectetur adipisicing elit. Accusantium quis,
    alias inventore distinctio laboriosam, quisquam nemo excepturi ipsum
    necessitatibus quia, iusto illum cupiditate eius corporis labore provident
    dignissimos? Iste, dignissimos.
  </p>
  <p>
    Lorem ipsum dolor sit amet consectetur adipisicing elit. Accusantium quis,
    alias inventore distinctio laboriosam, quisquam nemo excepturi ipsum
    necessitatibus quia, iusto illum cupiditate eius corporis labore provident
    dignissimos? Iste, dignissimos.
  </p>
  <h2>Second heading 2</h2>
  <p>
    Lorem ipsum dolor sit amet consectetur adipisicing elit. Nihil fugit,
    distinctio ex incidunt sint sed unde, perferendis, quos modi nulla dolore
    cumque delectus doloremque ab repudiandae earum nemo in adipisci.
  </p>
  <p>
    Lorem ipsum dolor sit amet consectetur adipisicing elit. Accusantium quis,
    alias inventore distinctio laboriosam, quisquam nemo excepturi ipsum
    necessitatibus quia, iusto illum cupiditate eius corporis labore provident
    dignissimos? Iste, dignissimos.
  </p>
  <p>
    Lorem ipsum dolor sit amet consectetur adipisicing elit. Accusantium quis,
    alias inventore distinctio laboriosam, quisquam nemo excepturi ipsum
    necessitatibus quia, iusto illum cupiditate eius corporis labore provident
    dignissimos? Iste, dignissimos.
  </p>
  <h3>Heading 3 again</h3>
  <p>
    Lorem ipsum dolor sit amet consectetur adipisicing elit. Voluptates harum
    ipsum, expedita et reprehenderit error asperiores repudiandae aspernatur
    eum optio. Illo unde odit, inventore praesentium et quia voluptatum
    cupiditate similique?
  </p>
  <p>
    Lorem ipsum dolor sit amet consectetur adipisicing elit. Accusantium quis,
    alias inventore distinctio laboriosam, quisquam nemo excepturi ipsum
    necessitatibus quia, iusto illum cupiditate eius corporis labore provident
    dignissimos? Iste, dignissimos.
  </p>
  <p>
    Lorem ipsum dolor sit amet consectetur adipisicing elit. Accusantium quis,
    alias inventore distinctio laboriosam, quisquam nemo excepturi ipsum
    necessitatibus quia, iusto illum cupiditate eius corporis labore provident
    dignissimos? Iste, dignissimos.
  </p>
  <h4>Heading 4</h4>
  <p>
    Lorem ipsum dolor sit amet consectetur adipisicing elit. Voluptates harum
    ipsum, expedita et reprehenderit error asperiores repudiandae aspernatur
    eum optio. Illo unde odit, inventore praesentium et quia voluptatum
    cupiditate similique?
  </p>
  <p>
    Lorem ipsum dolor sit amet consectetur adipisicing elit. Accusantium quis,
    alias inventore distinctio laboriosam, quisquam nemo excepturi ipsum
    necessitatibus quia, iusto illum cupiditate eius corporis labore provident
    dignissimos? Iste, dignissimos.
  </p>
  <h5>Heading 5</h5>
  <p>
    Lorem ipsum dolor sit amet consectetur adipisicing elit. Voluptates harum
    ipsum, expedita et reprehenderit error asperiores repudiandae aspernatur
    eum optio. Illo unde odit, inventore praesentium et quia voluptatum
    cupiditate similique?
  </p>
  <p>
    Lorem ipsum dolor sit amet consectetur adipisicing elit. Accusantium quis,
    alias inventore distinctio laboriosam, quisquam nemo excepturi ipsum
    necessitatibus quia, iusto illum cupiditate eius corporis labore provident
    dignissimos? Iste, dignissimos.
  </p>
  <h6>Heading 6</h6>
  <p>
    Lorem ipsum dolor sit amet consectetur adipisicing elit. Voluptates harum
    ipsum, expedita et reprehenderit error asperiores repudiandae aspernatur
    eum optio. Illo unde odit, inventore praesentium et quia voluptatum
    cupiditate similique?
  </p>
  <p>
    Lorem ipsum dolor sit amet consectetur adipisicing elit. Accusantium quis,
    alias inventore distinctio laboriosam, quisquam nemo excepturi ipsum
    necessitatibus quia, iusto illum cupiditate eius corporis labore provident
    dignissimos? Iste, dignissimos.
  </p>
  <div id="snackbar">Link copied to clipboard</div>
!

CSS 

              
                @import url("https://fonts.googleapis.com/css2?family=Merriweather:wght@700&family=Poppins&display=swap");

body {
  margin: 0 auto;
  max-width: 600px;
  font-family: Poppins, sans-serif;
}

h1,
h2,
h3,
h4,
h5,
h6 {
  font-family: Merriweather, serif;
  font-weight: bold;
  display: flex;
  align-items: center;
}

:is(h2, h3, h4, h5, h6) button {
  text-decoration: none;
  color: #767676;
  margin: 0 0.25em;
  padding: 0.1em;
  font: inherit;
  font-size: 0.8em;
  transition: color 0.2s ease-in-out;
}

:is(h2, h3, h4, h5, h6) button:hover {
  color: rgb(27, 27, 252);
}

/* Position it at the top and in the middle of the screen */
#snackbar {
  position: fixed;
  z-index: 1;
  top: 0;
  left: 50%;
  min-width: 250px;
  margin-left: -125px;
  background-color: #333;
  color: #fff;
  text-align: center;
  border-radius: 5px;
  padding: 16px;
  transform: translateY(-10px);
  opacity: 0;
}
!

JS 

              
                let headings = document.querySelectorAll("h2, h3, h4, h5, h6");
let snackbarTimeout;

// we do this to exclude the text fragment
const currentURL = `${window.location.protocol}//${window.location.host}${window.location.pathname}`;

headings.forEach((heading) => {
  let slug = slugify(heading.innerText);
  heading.setAttribute("id", slug);

  const bookmarkBtn = document.createElement("button");
  bookmarkBtn.innerText = "#";
  bookmarkBtn.setAttribute("data-href", `${currentURL}#${slug}`);
  bookmarkBtn.addEventListener("click", copyLink);
  heading.append(bookmarkBtn);
});

/**
 * Produces a slug from the text provided that can be used as an URL fragment. Does it the same as GitHub.
 *
 * @param {string} text - The text to slugify
 * @returns {string} The slug.
 */
function slugify(text) {
  // Anything that is an unwanted punctuation character
  const PUNCTUATION_REGEXP = /[^\p{L}\p{M}\p{N}\p{Pc}\- ]/gu;

  let slug = text.trim().toLowerCase();
  slug = slug.replace(PUNCTUATION_REGEXP, "").replace(/ /g, "-");
  return slug;
}

async function copyLink(event) {
  const button = event.srcElement;
  let text = button.getAttribute("data-href");
  await navigator.clipboard.writeText(text);
  showSnackbar();
}

function showSnackbar() {
  let snackbar = document.getElementById("snackbar");

  let fadeIn = snackbar
    .animate(
      [
        { opacity: 1, offset: 0.1 },
        { opacity: 1, offset: 0.8 },
        { opacity: 0, offset: 1 }
      ],
      {
        duration: 3000
      }
    )
    .play();

  let move = snackbar
    .animate(
      [
        { transform: "translateY(20px)", offset: 0.2 },
        { transform: "translateY(20px)", offset: 0.8 },
        { transform: "translateY(-10px)", offset: 1 }
      ],
      {
        duration: 3000
      }
    )
    .play();
}
!
999px

Console