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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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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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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.

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HTML 

              
                <ul id="accordion" class="accordion">
  <li class="accordion__item">
    <span class="accordion__header">Question 1?</span>
    <div class="accordion__panel">
      <h3>Question 1?</h3>
      <ul class="accordion__body">
        <li>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Mauris ligula elit, congue vel nulla ut, ullamcorper ullamcorper eros. Proin molestie viverra odio vitae euismod. In a diam quam. Pellentesque sit amet urna et libero sollicitudin interdum. Duis et tellus diam. Mauris tempus nec tortor maximus fringilla. Aenean ultricies quam id nunc posuere, ac iaculis dui tristique. Sed sit amet sem sed nulla sollicitudin vulputate tristique sit amet odio. Ut tempus, nulla eu tempor tempus, felis leo ultrices felis, vitae elementum ligula dui eu nisl. Aliquam dignissim mi orci, eu congue ipsum sollicitudin ut.
        </li>
      </ul>
    </div>
  </li>
  <li class="accordion__item">
    <span class="accordion__header">Question 2?</span>    
    <div class="accordion__panel">
      <h3>Question 2?</h3>
      <ul class="accordion__body">
        <li>Sed sed dolor accumsan, imperdiet elit in, egestas nisl. Curabitur faucibus purus felis, eu posuere libero rutrum vel. Phasellus eget mauris lacinia, commodo diam eu, fermentum nunc. Suspendisse potenti. Sed orci erat, tempor ac neque hendrerit, rhoncus sodales ante. Donec maximus iaculis vestibulum. In dictum consectetur ligula, in placerat sem varius in. Quisque ac justo felis. Aliquam semper rutrum auctor. Nunc a ipsum fermentum, molestie libero non, porta urna.
        </li>
      </ul>
    </div>
  </li>
  <li class="accordion__item">
    <span class="accordion__header">Question 3?</span>
    <div class="accordion__panel">
      <h3>Question 3?</h3>
      <ul class="accordion__body">
        <li>Nunc a urna libero. Morbi sit amet neque et purus viverra viverra vel sit amet nisl. Quisque eu orci nisl. Nunc varius dolor erat. Integer tellus eros, vestibulum in lobortis id, cursus feugiat ex. Suspendisse dapibus, metus at suscipit hendrerit, justo quam vestibulum est, vel tristique odio massa nec dui. Nunc convallis placerat laoreet. Maecenas nunc enim, pretium at elit eget, interdum fringilla purus. Pellentesque molestie libero vitae justo lacinia, at ornare lectus volutpat. Pellentesque ac posuere dui. Suspendisse aliquet lobortis viverra. In tincidunt vulputate nisl, et hendrerit dui fermentum non. Maecenas venenatis pellentesque arcu non maximus.
        </li>
      </ul>
    </div>
  </li>
</ul>
!

CSS 

              
                .accordion {
  list-style: none;
  margin: 1rem;
  padding: 0;
  
  &__item {
    color: #6505cc;
    background: #eedbff;
    border: 1px solid;
    border-bottom: 0;
    
    &:last-child {
      border-bottom: 1px solid;
    }
  }
  
  &__header {
    display: block;
    position: relative;
    padding: 0.5rem 1rem;
    text-transform: uppercase;
    font-weight: bold;
    
    &::after {
      content: '';
      position: absolute;
      right: 1rem;
      width: 0px;
      height: 0px;
      border-left: 10px solid transparent;
      border-right: 10px solid transparent;
      border-top: 15px solid #6505cc;
    }
  }
  
  &__panel {
    padding: 1rem;
    border-top: 1px solid;
    
    h3 {
      margin-top: 0;
    }
  }
  
  &__body {
    list-style: none;
    padding: 0;
  }
}
!

JS
!
999px

Console