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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

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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

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HTML 

              
                <div class="header">added some space here to show that it works even with elements placed above the nav</div>
<div id="app"></div>
<div class="content">
  <div>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Provident aliquam itaque, ab optio, omnis cupiditate ut accusamus alias, quae vitae ducimus animi autem aperiam qui in asperiores dolorum? Adipisci, sit!</div>
  <div>Dolorem nesciunt enim odit, voluptate maxime corporis, odio assumenda provident neque dolor atque minima ad! At rem laborum ullam deserunt in est veniam asperiores corrupti, ea optio, magni fugiat nulla.</div>
  <div>Qui, quo sunt fuga autem beatae animi error nemo commodi ipsam dolore, mollitia dolorem atque, quas nesciunt? At, nam quaerat accusantium adipisci explicabo nulla a quidem quas ea fugiat esse?</div>
  <div>Quam aut, excepturi eveniet illum facere officia doloremque et ullam iusto. Iure cum sapiente, culpa nobis nemo accusamus tempora voluptatibus, id odit impedit officia itaque totam. Deserunt nemo voluptates nihil!</div>
  <div>Minus quaerat, blanditiis impedit quam fugiat nostrum maxime quisquam. Laboriosam nostrum accusantium saepe exercitationem, temporibus blanditiis facere non iusto enim repellendus suscipit corporis eveniet commodi maxime nihil tenetur itaque voluptatibus.</div>
  <div>Veniam quos error mollitia molestias esse sapiente cumque fugiat id obcaecati ex repellat optio eaque commodi nam nesciunt beatae tempore, autem illum aspernatur vero et numquam. Laborum animi similique quos.</div>
  <div>Eveniet quasi est voluptates minima, ipsum possimus consectetur. Quo, vel. Qui, beatae unde at amet illo tempore molestias saepe quidem quo voluptatum. Ea amet cum doloremque eos iste accusamus sunt!</div>
  <div>Lorem ipsum dolor sit amet consectetur adipisicing elit. Voluptatem rem vel explicabo consequatur perspiciatis accusamus esse, eligendi, alias eum ad veniam, fuga minima nisi expedita eius! Officia vel ullam laudantium?</div>
  <div>Dolore temporibus quidem velit, soluta eligendi voluptatibus, adipisci labore id non reiciendis libero alias in a omnis asperiores recusandae atque cum nisi repellendus error itaque? Numquam molestias ab labore aliquid.</div>
  <div>Aliquid sequi rem quasi facere alias quae, optio soluta adipisci illum dolore vitae? Ipsum, provident iure aliquid ut aspernatur, non, sint necessitatibus itaque veniam voluptas eos temporibus asperiores voluptatum vero.</div>
  <div>Porro laudantium fugit aperiam hic explicabo cupiditate dicta dolorum, corrupti ipsam sed labore adipisci maiores voluptates tenetur. Explicabo, voluptates. Rerum alias quis facere quia saepe aperiam molestiae iusto ea modi.</div>
  <div>Dolore possimus ipsa, praesentium iusto, esse sed, qui reprehenderit incidunt sequi eveniet cum. Aspernatur architecto doloremque eius quaerat alias debitis blanditiis harum, nesciunt modi quae maiores quo dolorum numquam omnis.</div>
  <div>Reiciendis corporis quo doloribus tempora enim exercitationem possimus iure alias qui illo, totam culpa voluptas laudantium beatae. Voluptatibus, saepe? Perferendis possimus explicabo id et assumenda aut consequuntur animi officiis facilis?</div>
  <div>Error, eligendi molestiae quaerat dolorum quidem vitae nulla maiores adipisci corrupti laudantium eos magni, nesciunt, accusantium iste dolore vero libero fugiat perspiciatis. Odio voluptate asperiores repellat maiores nemo accusamus esse.</div>
</div>
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CSS 

              
                body {
  margin: 0;
  padding: 0;
}

.header {
  padding: 20px
}

nav {
  width: 100%;
  margin: 0;
  top: 0;
  background: #212121;
  color: #ccc;
}

ul {
  list-style: none;
  display: flex;
  margin: 0;
  padding: 0;
}

li {
  height: 100%;
  flex: 1;
  text-align: center;
  display: flex;
  justify-content: center;
  align-items: center;
  padding: 10px;
  transition: all 0.3s ease-in;
  cursor: pointer;
}

li:hover {
  background: #848484;
  color: #212121;
}

.fixed-nav {
  position: fixed;
}

.content {
  width: 80%;
  margin: 0 auto;
  text-align: justify;
  padding-top: 20px;
}

.content > div {
  margin: 10px 0;
}
!

JS 

              
                class Nav extends React.Component {
  constructor(props) {
		super(props);

		this.state = {};

		this.handleScroll = this.handleScroll.bind(this);
	}

	handleScroll() {
		this.setState({scroll: window.scrollY});
	}
  
  componentDidMount() {
		const el = document.querySelector('nav');
		this.setState({top: el.offsetTop, height: el.offsetHeight});
		window.addEventListener('scroll', this.handleScroll);
	}
  
  componentDidUpdate() {
		this.state.scroll > this.state.top ? 
			document.body.style.paddingTop = `${this.state.height}px` :
			document.body.style.paddingTop = 0;
	}
  
  render() {
    return (
      <nav className={this.state.scroll > this.state.top ? "fixed-nav" : ""}>
        <ul>
          <li>Home</li>
          <li>About</li>
          <li>Careers</li>
          <li>Contact</li>
          <li>Help</li>
        </ul>
      </nav>
    );
  }
}

React.render(<Nav />, document.getElementById('app'));
!
999px

Console