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HTML

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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

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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

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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).

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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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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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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="container">
  <!-- Tabs -->
  <ul id="nav-tab" class="nav">
    <li class="active"><a href="#home">Home</a></li>
    <li><a href="#profile">Profile</a></li>
    <li><a href="#messages">Messages</a></li>
    <li><a href="#settings">Settings</a></li>
  </ul>

  <!-- Tab panes -->
  <div class="tab-content">
    <div class="tab-pane active" id="home">
      <h4>Home Panel Content</h4> 
      <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Quidem iure quos cum, saepe reprehenderit minima quasi architecto numquam nesciunt dicta. Qui excepturi recusandae vitae maiores, inventore sequi? Rerum, odio omnis.</p> </div>
    <div class="tab-pane" id="profile">
      <h4>Profile Panel</h4>
      <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Quidem iure quos cum, saepe reprehenderit minima quasi architecto numquam nesciunt dicta. Qui excepturi recusandae vitae maiores, inventore sequi? Rerum, odio omnis. Lorem ipsum dolor sit amet consectetur adipisicing elit. Alias distinctio, tempora incidunt aliquid adipisci, minus rerum optio libero quae provident sed at dignissimos, quia nostrum! Fuga dolorum quia hic magni.</p></div>
    <div class="tab-pane" id="messages">
      <h4>Messages Panel</h4>
      <p>Lorem ipsum dolor sit amet consectetur, adipisicing elit. Fugiat quos, at qui aspernatur minus animi hic sunt necessitatibus incidunt molestiae reprehenderit ratione neque odit ipsa. Nemo laborum consequatur adipisci beatae!</p>
    </div>
    <div class="tab-pane" id="settings">
      <h4>Settings Panel</h4>
      <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Minima possimus sed odit iste vitae, magnam amet illum laudantium ea! Fugiat consectetur consequuntur qui eos obcaecati sequi ipsam repellat vero voluptate.</p>
    </div>
  </div>
</div>
!

CSS 

              
                body {
 font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";
  color: #444;
}

.container {
  max-width: 800px;
  margin: 0 auto;
}

ul {
  list-style: none;
  padding: 0;
  
  li {
    display: inline-flex;
    
    a {
      text-decoration: none;
      color: darkgray;
      padding: 10px;
      transition: all .3s ease-in-out;
      border-bottom: 1px solid transparent;
      &:hover {
        color: gray;
      }
    }
  }
}

.nav .active a { 
  color: slateblue; 
  border-bottom: 1px solid slateblue;
  &:hover {
    border-color: transparent;
    background: slateblue;
    color: white;
  }
}

.tab-pane { 
  display: none;
}

.tab-pane.active { 
  display: block; 
}
!

JS 

              
                /* Let's Build: With JavaScript - Web-Crunch.com
   Subscribe on YouTube - https://youtube.com/c/webcrunch
   
   Let's Build: Dynamic Tabs 
*/

function onTabClick(event) {
  let activeTabs = document.querySelectorAll('.active');
  
  // deactivate existing active tab and panel
  // for( let i = 0; i < activeTabs.length; i++) {
  //   activeTabs[i].className = activeTabs[i].className.replace('active', '');
  // }
  
  activeTabs.forEach(function(tab) {
    tab.className = tab.className.replace('active', '');
  });
  
  // activate new tab and panel
  event.target.parentElement.className += ' active';
  document.getElementById(event.target.href.split('#')[1]).className += ' active';
}

const element = document.getElementById('nav-tab');

element.addEventListener('click', onTabClick, false);
!
999px

Console