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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

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>

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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-.

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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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HTML 

              
                <div>
  <ul>
    <li>
      <a href="#firstSection">Smooth scrolling to first section</a>
    </li>
    <li>
      <a href="#secondSection">Smooth scrolling second section</a>
    </li>
    <li>
      <a href="#thirdSection">Smooth scrolling third section</a>
    </li>
  </ul>

  <h2 id="firstSection">First section</h2>
  <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Ut vitae nunc sit amet urna congue ornare. Nullam dapibus bibendum purus blandit rhoncus. Pellentesque nisi justo, auctor vitae faucibus vehicula, rutrum sed massa. Fusce eget mauris id massa sollicitudin posuere vitae ut ligula. Integer imperdiet dui at neque porta auctor. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Curabitur sed felis vel dolor feugiat tincidunt. Maecenas nisi enim, dictum a molestie a, malesuada ut dolor. Aliquam non dolor consectetur, dictum augue eget, dapibus diam. Mauris eu suscipit est. Suspendisse rhoncus accumsan ullamcorper. Vivamus metus elit, sagittis eget suscipit nec, facilisis vel tellus. Maecenas sit amet augue faucibus, dictum dolor at, ullamcorper est.</p>

  <p>Nunc aliquam, velit ac hendrerit laoreet, velit eros efficitur sem, vitae luctus ligula elit at nisl. Nullam vulputate convallis ante, at volutpat augue finibus eu. Sed convallis mollis ante sit amet dictum. Etiam iaculis felis neque, a ultrices mauris hendrerit at. Ut in pharetra turpis. Proin sit amet justo lacinia, aliquam sapien et, pharetra libero. Vivamus quis lectus in eros finibus cursus consectetur at sem. Pellentesque eu semper odio. Suspendisse scelerisque cursus placerat.</p>

  <p>Interdum et malesuada fames ac ante ipsum primis in faucibus. Cras volutpat diam eu tellus faucibus, in semper orci euismod. Nunc auctor sapien semper ex tristique, non imperdiet nulla pellentesque. Fusce non eros dui. Duis id nunc at neque vulputate tristique. Sed molestie nulla hendrerit fringilla cursus. Nunc finibus suscipit diam vitae accumsan. Nam sodales dolor in arcu gravida, id blandit lectus maximus. Vestibulum ante ipsum primis in faucibus orci luctus et ultrices posuere cubilia curae; Donec nec suscipit arcu, vitae aliquam sem. Duis at eleifend diam. Curabitur venenatis facilisis leo, et molestie nisl semper id. Ut in leo nisl. Sed quis malesuada turpis, in vestibulum nulla.</p>

  <h2 id="secondSection">Second section</h2>
  <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Ut vitae nunc sit amet urna congue ornare. Nullam dapibus bibendum purus blandit rhoncus. Pellentesque nisi justo, auctor vitae faucibus vehicula, rutrum sed massa. Fusce eget mauris id massa sollicitudin posuere vitae ut ligula. Integer imperdiet dui at neque porta auctor. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Curabitur sed felis vel dolor feugiat tincidunt. Maecenas nisi enim, dictum a molestie a, malesuada ut dolor. Aliquam non dolor consectetur, dictum augue eget, dapibus diam. Mauris eu suscipit est. Suspendisse rhoncus accumsan ullamcorper. Vivamus metus elit, sagittis eget suscipit nec, facilisis vel tellus. Maecenas sit amet augue faucibus, dictum dolor at, ullamcorper est.</p>

  <p>Nunc aliquam, velit ac hendrerit laoreet, velit eros efficitur sem, vitae luctus ligula elit at nisl. Nullam vulputate convallis ante, at volutpat augue finibus eu. Sed convallis mollis ante sit amet dictum. Etiam iaculis felis neque, a ultrices mauris hendrerit at. Ut in pharetra turpis. Proin sit amet justo lacinia, aliquam sapien et, pharetra libero. Vivamus quis lectus in eros finibus cursus consectetur at sem. Pellentesque eu semper odio. Suspendisse scelerisque cursus placerat.</p>

  <p>Interdum et malesuada fames ac ante ipsum primis in faucibus. Cras volutpat diam eu tellus faucibus, in semper orci euismod. Nunc auctor sapien semper ex tristique, non imperdiet nulla pellentesque. Fusce non eros dui. Duis id nunc at neque vulputate tristique. Sed molestie nulla hendrerit fringilla cursus. Nunc finibus suscipit diam vitae accumsan. Nam sodales dolor in arcu gravida, id blandit lectus maximus. Vestibulum ante ipsum primis in faucibus orci luctus et ultrices posuere cubilia curae; Donec nec suscipit arcu, vitae aliquam sem. Duis at eleifend diam. Curabitur venenatis facilisis leo, et molestie nisl semper id. Ut in leo nisl. Sed quis malesuada turpis, in vestibulum nulla.</p>

  <h2 id="thirdSection">Third section</h2>
  <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Ut vitae nunc sit amet urna congue ornare. Nullam dapibus bibendum purus blandit rhoncus. Pellentesque nisi justo, auctor vitae faucibus vehicula, rutrum sed massa. Fusce eget mauris id massa sollicitudin posuere vitae ut ligula. Integer imperdiet dui at neque porta auctor. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Curabitur sed felis vel dolor feugiat tincidunt. Maecenas nisi enim, dictum a molestie a, malesuada ut dolor. Aliquam non dolor consectetur, dictum augue eget, dapibus diam. Mauris eu suscipit est. Suspendisse rhoncus accumsan ullamcorper. Vivamus metus elit, sagittis eget suscipit nec, facilisis vel tellus. Maecenas sit amet augue faucibus, dictum dolor at, ullamcorper est.</p>

  <p>Nunc aliquam, velit ac hendrerit laoreet, velit eros efficitur sem, vitae luctus ligula elit at nisl. Nullam vulputate convallis ante, at volutpat augue finibus eu. Sed convallis mollis ante sit amet dictum. Etiam iaculis felis neque, a ultrices mauris hendrerit at. Ut in pharetra turpis. Proin sit amet justo lacinia, aliquam sapien et, pharetra libero. Vivamus quis lectus in eros finibus cursus consectetur at sem. Pellentesque eu semper odio. Suspendisse scelerisque cursus placerat.</p>

  <p>Interdum et malesuada fames ac ante ipsum primis in faucibus. Cras volutpat diam eu tellus faucibus, in semper orci euismod. Nunc auctor sapien semper ex tristique, non imperdiet nulla pellentesque. Fusce non eros dui. Duis id nunc at neque vulputate tristique. Sed molestie nulla hendrerit fringilla cursus. Nunc finibus suscipit diam vitae accumsan. Nam sodales dolor in arcu gravida, id blandit lectus maximus. Vestibulum ante ipsum primis in faucibus orci luctus et ultrices posuere cubilia curae; Donec nec suscipit arcu, vitae aliquam sem. Duis at eleifend diam. Curabitur venenatis facilisis leo, et molestie nisl semper id. Ut in leo nisl. Sed quis malesuada turpis, in vestibulum nulla.</p>
</div>
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CSS 

              
                html {
  scroll-behavior: smooth;
  font-family: 'Source Sans Pro', sans-serif;
}

ul {
  list-style: none;
  padding-left: 0;
  
  li {
    a {
      color: #000;
      text-decoration: underline;
    }
  }
}
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JS
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999px

Console