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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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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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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.

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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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Visit your global Editor Settings.

HTML 

              
                <main>
<nav>
  Here's where your TOC would go.
</nav>
<article>
  Here are some docs, where you are told how to install something.
  <deploy-docs-commands enhanced="✨">
    <deploy-docs-command>
      <pre class="hljs"><code data-language="bash"><span class="code-line">npm i --global @begin/deploy</span></code></pre>
    </deploy-docs-command>
    <deploy-docs-command os="win" class="hidden">
      <pre class="hljs hljs-unregistered"><code data-language="">npm i --global "@begin/deploy"</code></pre>
    </deploy-docs-command>
  </deploy-docs-commands>
  
  Then later on down the page you are given further instructions on how to do more stuff. Notice that if you flipped the OS selector switch above it is reflected here in the second code block.

  <deploy-docs-commands enhanced="✨">
    <deploy-docs-command>
      <pre class="hljs"><code data-language="bash"><span class="code-line">begin deploy</span></code></pre>
    </deploy-docs-command>
    <deploy-docs-command os="win" class="hidden">
      <pre class="hljs hljs-unregistered"><code data-language="">npx begin deploy</code></pre>
    </deploy-docs-command>
  </deploy-docs-commands>
</article>
  </main>
!

CSS 

              
                .hidden {
  display: none;
}

article {
  max-width: 600px;
}

main {
  display: flex;
  gap: 5px;
}

nav {
  max-width: 300px;
  background-color: hsl(0deg 0% 50% / 0.125);
}
!

JS 

              
                /* globals document window HTMLElement SpeechSynthesisUtterance customElements */
const template = document.createElement('template');
template.innerHTML = `
<style>
    :host {
      display: block;
      margin-block: var(--space-0);
    }

    .toggle input {
      display: none;
    }

    :host > div {
      background-color: hsl(0deg 0% 50% / 0.125);
      text-align: end;
    }

    label {
      cursor: pointer;
      font-weight: 500;
      color: var(--accent);
      display: inline-flex;
      align-items: center;
      gap: clamp(0.4rem, 0.44rem + -0.18vw, 0.27rem);
      font-size: clamp(0.83rem, 0.82rem + 0.07vw, 0.89rem);
    }

    svg {
      aspect-ratio: 1 / 1;
      height: 1rem;
      color: var(--fore);
    }

    .slider {
      width: 32px;
      height: 16px;
      border-radius: 1rem;
      background-color: lightblue;
      transform: scale(1);
    }

    .slider:before {
      position: absolute;
      width: 14px;
      height: 14px;
      top: 1px;
      bottom: 1px;
      left: 1px;
      content: '';
      background-color: white;
      border-radius: 50%;
      transition: transform 0.15s ease-in-out;
    }

    input:checked + .slider:before {
      transform: translateX(1rem);
    }
  </style>

  <slot></slot>

  <div class='text-end pbs-6 pi-4'>
    <label class="toggle inline-flex gap-5 align-items-center text-1">
      <svg id="icon-apple" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 384 512"><!--! Font Awesome Pro 6.2.1 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license (Commercial License) Copyright 2022 Fonticons, Inc. --><path fill="currentColor" d="M318.7 268.7c-.2-36.7 16.4-64.4 50-84.8-18.8-26.9-47.2-41.7-84.7-44.6-35.5-2.8-74.3 20.7-88.5 20.7-15 0-49.4-19.7-76.4-19.7C63.3 141.2 4 184.8 4 273.5q0 39.3 14.4 81.2c12.8 36.7 59 126.7 107.2 125.2 25.2-.6 43-17.9 75.8-17.9 31.8 0 48.3 17.9 76.4 17.9 48.6-.7 90.4-82.5 102.6-119.3-65.2-30.7-61.7-90-61.7-91.9zm-56.6-164.2c27.3-32.4 24.8-61.9 24-72.5-24.1 1.4-52 16.4-67.9 34.9-17.5 19.8-27.8 44.3-25.6 71.9 26.1 2 49.9-11.4 69.5-34.3z"/>
      </svg>
      <svg id="icon-linux" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 448 512"><!--! Font Awesome Pro 6.2.1 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license (Commercial License) Copyright 2022 Fonticons, Inc. --><path fill="currentColor" d="M220.8 123.3c1 .5 1.8 1.7 3 1.7 1.1 0 2.8-.4 2.9-1.5.2-1.4-1.9-2.3-3.2-2.9-1.7-.7-3.9-1-5.5-.1-.4.2-.8.7-.6 1.1.3 1.3 2.3 1.1 3.4 1.7zm-21.9 1.7c1.2 0 2-1.2 3-1.7 1.1-.6 3.1-.4 3.5-1.6.2-.4-.2-.9-.6-1.1-1.6-.9-3.8-.6-5.5.1-1.3.6-3.4 1.5-3.2 2.9.1 1 1.8 1.5 2.8 1.4zM420 403.8c-3.6-4-5.3-11.6-7.2-19.7-1.8-8.1-3.9-16.8-10.5-22.4-1.3-1.1-2.6-2.1-4-2.9-1.3-.8-2.7-1.5-4.1-2 9.2-27.3 5.6-54.5-3.7-79.1-11.4-30.1-31.3-56.4-46.5-74.4-17.1-21.5-33.7-41.9-33.4-72C311.1 85.4 315.7.1 234.8 0 132.4-.2 158 103.4 156.9 135.2c-1.7 23.4-6.4 41.8-22.5 64.7-18.9 22.5-45.5 58.8-58.1 96.7-6 17.9-8.8 36.1-6.2 53.3-6.5 5.8-11.4 14.7-16.6 20.2-4.2 4.3-10.3 5.9-17 8.3s-14 6-18.5 14.5c-2.1 3.9-2.8 8.1-2.8 12.4 0 3.9.6 7.9 1.2 11.8 1.2 8.1 2.5 15.7.8 20.8-5.2 14.4-5.9 24.4-2.2 31.7 3.8 7.3 11.4 10.5 20.1 12.3 17.3 3.6 40.8 2.7 59.3 12.5 19.8 10.4 39.9 14.1 55.9 10.4 11.6-2.6 21.1-9.6 25.9-20.2 12.5-.1 26.3-5.4 48.3-6.6 14.9-1.2 33.6 5.3 55.1 4.1.6 2.3 1.4 4.6 2.5 6.7v.1c8.3 16.7 23.8 24.3 40.3 23 16.6-1.3 34.1-11 48.3-27.9 13.6-16.4 36-23.2 50.9-32.2 7.4-4.5 13.4-10.1 13.9-18.3.4-8.2-4.4-17.3-15.5-29.7zM223.7 87.3c9.8-22.2 34.2-21.8 44-.4 6.5 14.2 3.6 30.9-4.3 40.4-1.6-.8-5.9-2.6-12.6-4.9 1.1-1.2 3.1-2.7 3.9-4.6 4.8-11.8-.2-27-9.1-27.3-7.3-.5-13.9 10.8-11.8 23-4.1-2-9.4-3.5-13-4.4-1-6.9-.3-14.6 2.9-21.8zM183 75.8c10.1 0 20.8 14.2 19.1 33.5-3.5 1-7.1 2.5-10.2 4.6 1.2-8.9-3.3-20.1-9.6-19.6-8.4.7-9.8 21.2-1.8 28.1 1 .8 1.9-.2-5.9 5.5-15.6-14.6-10.5-52.1 8.4-52.1zm-13.6 60.7c6.2-4.6 13.6-10 14.1-10.5 4.7-4.4 13.5-14.2 27.9-14.2 7.1 0 15.6 2.3 25.9 8.9 6.3 4.1 11.3 4.4 22.6 9.3 8.4 3.5 13.7 9.7 10.5 18.2-2.6 7.1-11 14.4-22.7 18.1-11.1 3.6-19.8 16-38.2 14.9-3.9-.2-7-1-9.6-2.1-8-3.5-12.2-10.4-20-15-8.6-4.8-13.2-10.4-14.7-15.3-1.4-4.9 0-9 4.2-12.3zm3.3 334c-2.7 35.1-43.9 34.4-75.3 18-29.9-15.8-68.6-6.5-76.5-21.9-2.4-4.7-2.4-12.7 2.6-26.4v-.2c2.4-7.6.6-16-.6-23.9-1.2-7.8-1.8-15 .9-20 3.5-6.7 8.5-9.1 14.8-11.3 10.3-3.7 11.8-3.4 19.6-9.9 5.5-5.7 9.5-12.9 14.3-18 5.1-5.5 10-8.1 17.7-6.9 8.1 1.2 15.1 6.8 21.9 16l19.6 35.6c9.5 19.9 43.1 48.4 41 68.9zm-1.4-25.9c-4.1-6.6-9.6-13.6-14.4-19.6 7.1 0 14.2-2.2 16.7-8.9 2.3-6.2 0-14.9-7.4-24.9-13.5-18.2-38.3-32.5-38.3-32.5-13.5-8.4-21.1-18.7-24.6-29.9s-3-23.3-.3-35.2c5.2-22.9 18.6-45.2 27.2-59.2 2.3-1.7.8 3.2-8.7 20.8-8.5 16.1-24.4 53.3-2.6 82.4.6-20.7 5.5-41.8 13.8-61.5 12-27.4 37.3-74.9 39.3-112.7 1.1.8 4.6 3.2 6.2 4.1 4.6 2.7 8.1 6.7 12.6 10.3 12.4 10 28.5 9.2 42.4 1.2 6.2-3.5 11.2-7.5 15.9-9 9.9-3.1 17.8-8.6 22.3-15 7.7 30.4 25.7 74.3 37.2 95.7 6.1 11.4 18.3 35.5 23.6 64.6 3.3-.1 7 .4 10.9 1.4 13.8-35.7-11.7-74.2-23.3-84.9-4.7-4.6-4.9-6.6-2.6-6.5 12.6 11.2 29.2 33.7 35.2 59 2.8 11.6 3.3 23.7.4 35.7 16.4 6.8 35.9 17.9 30.7 34.8-2.2-.1-3.2 0-4.2 0 3.2-10.1-3.9-17.6-22.8-26.1-19.6-8.6-36-8.6-38.3 12.5-12.1 4.2-18.3 14.7-21.4 27.3-2.8 11.2-3.6 24.7-4.4 39.9-.5 7.7-3.6 18-6.8 29-32.1 22.9-76.7 32.9-114.3 7.2zm257.4-11.5c-.9 16.8-41.2 19.9-63.2 46.5-13.2 15.7-29.4 24.4-43.6 25.5s-26.5-4.8-33.7-19.3c-4.7-11.1-2.4-23.1 1.1-36.3 3.7-14.2 9.2-28.8 9.9-40.6.8-15.2 1.7-28.5 4.2-38.7 2.6-10.3 6.6-17.2 13.7-21.1.3-.2.7-.3 1-.5.8 13.2 7.3 26.6 18.8 29.5 12.6 3.3 30.7-7.5 38.4-16.3 9-.3 15.7-.9 22.6 5.1 9.9 8.5 7.1 30.3 17.1 41.6 10.6 11.6 14 19.5 13.7 24.6zM173.3 148.7c2 1.9 4.7 4.5 8 7.1 6.6 5.2 15.8 10.6 27.3 10.6 11.6 0 22.5-5.9 31.8-10.8 4.9-2.6 10.9-7 14.8-10.4s5.9-6.3 3.1-6.6-2.6 2.6-6 5.1c-4.4 3.2-9.7 7.4-13.9 9.8-7.4 4.2-19.5 10.2-29.9 10.2s-18.7-4.8-24.9-9.7c-3.1-2.5-5.7-5-7.7-6.9-1.5-1.4-1.9-4.6-4.3-4.9-1.4-.1-1.8 3.7 1.7 6.5z"/>
      </svg>
      <input type="checkbox" name="toggle-windows" value="windows" role="toggle" aria-label="Toggle Windows" />
      <div class="slider relative round inline-block"></div>
      <svg id="icon-windows" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 448 512"><!--! Font Awesome Pro 6.2.1 by @fontawesome - https://fontawesome.com License - https://fontawesome.com/license (Commercial License) Copyright 2022 Fonticons, Inc. --><path fill="currentColor" d="M0 93.7l183.6-25.3v177.4H0V93.7zm0 324.6l183.6 25.3V268.4H0v149.9zm203.8 28L448 480V268.4H203.8v177.9zm0-380.6v180.1H448V32L203.8 65.7z"/>
      </svg>
    </label>
  </div>
`

const PREFERRED_OS_KEY = 'preferredOs'

class DocsCommands extends HTMLElement {

  constructor() {
    super();
    const shadowRoot = this.attachShadow({ mode: 'open' });
    shadowRoot.appendChild(template.content.cloneNode(true));
  }

  connectedCallback() {
    this.winInput = this.shadowRoot.querySelector('input[type="checkbox"]')
    this.codeBlock = this.querySelector('deploy-docs-command:not([os])')
    this.winCodeBlock = this.querySelector('deploy-docs-command[os="win"]')
    
    this.onOsChange = this.onOsChange.bind(this)
    this.onSwitchChange = this.onSwitchChange.bind(this)

    const preferredOs = window.localStorage.getItem(PREFERRED_OS_KEY)
    this.update(preferredOs === 'win')

    this.addEventListener('preferWinChange', this.onOsChange)
    this.winInput.addEventListener('change', this.onSwitchChange)
  }

  disconnectedCallback() {
    this.removeEventListener('preferWinChange', this.onOsChange)
    this.winInput.removeEventListener('change', this.onSwitchChange)
  }

  onOsChange(e) {
    this.update(e.detail)
  }

  onSwitchChange(e) {
    const preferWin = e.srcElement.checked

    if (preferWin) {
      window.localStorage.setItem(PREFERRED_OS_KEY, 'win')
    } else {
      window.localStorage.removeItem(PREFERRED_OS_KEY)
    }

    const event = new CustomEvent('preferWinChange', { detail: preferWin })
    for (const elem of document.querySelectorAll('deploy-docs-commands')) {
      elem.dispatchEvent(event)
    }
  }

  update(preferWin) {
    this.winInput.checked = preferWin
    
    if (preferWin) {
      this.codeBlock.classList.add('hidden')
      this.winCodeBlock.classList.remove('hidden')

    } else {
      this.winCodeBlock.classList.add('hidden')
      this.codeBlock.classList.remove('hidden')
    }
  }
}

customElements.define('deploy-docs-commands', DocsCommands)
!
999px

Console