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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>

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).

Add External Stylesheets/Pens

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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.

All packages are different, so refer to their docs for how they work.

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HTML 

              
                <div class="article">
  <h1>Create sections with alternating backgrounds using <code>&lt;hr&gt;</code></h1>
  <hr>
  <p>Every time an <code>&lt;hr&gt;</code> element is added, the background alternates creating awesome sections.</p>
  <hr>
  <p>This could be used as an easy way to create sections without additional divs and markup in, say, a WordPress theme.</p>
  <hr>
  <p>This <del>does not work in any version of</del> now works in Internet Explorer 9+ and falls back nicely.</p>
  <hr>
  <h2>Here's an example of a section</h2>
  <p> A paragraph. Praesent commodo cursus magna, vel scelerisque nisl consectetur et. Donec sed odio dui. Vivamus sagittis lacus vel augue laoreet rutrum faucibus dolor auctor. Nullam quis risus eget urna mollis ornare vel eu leo. Cum sociis natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus.</p>
  <p>Praesent commodo cursus magna, vel scelerisque nisl consectetur et. Vivamus sagittis lacus vel augue laoreet rutrum faucibus dolor auctor. Donec sed odio dui. Fusce dapibus, tellus ac cursus commodo, tortor mauris condimentum nibh, ut fermentum massa justo sit amet risus. Maecenas faucibus mollis interdum.</p>
  <p>Cras justo odio, dapibus ac facilisis in, egestas eget quam. Donec sed odio dui. Maecenas sed diam eget risus varius blandit sit amet non magna. Vestibulum id ligula porta felis euismod semper.</p>
  <hr>
  <img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/5247/city.jpg" alt="city" />
  <hr>
  <h2>Here's an example of another section</h2>
  <img class="align-left" src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/5247/city.jpg" alt="city" />
  <p> A paragraph. Nullam id dolor id nibh ultricies vehicula ut id elit. Duis mollis, est non commodo luctus, nisi erat porttitor ligula, eget lacinia odio sem nec elit. Nulla vitae elit libero, a pharetra augue. Maecenas sed diam eget risus varius blandit sit amet non magna.</p>
  <p>Aenean lacinia bibendum nulla sed consectetur. Cras justo odio, dapibus ac facilisis in, egestas eget quam. Sed posuere consectetur est at lobortis. Curabitur blandit tempus porttitor. Integer posuere erat a ante venenatis dapibus posuere velit aliquet.</p>
  <p>Praesent commodo cursus magna, vel scelerisque nisl consectetur et. Nulla vitae elit libero, a pharetra augue. Etiam porta sem malesuada magna mollis euismod. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Integer posuere erat a ante venenatis dapibus posuere velit aliquet. Donec id elit non mi porta gravida at eget metus.</p>
  <select name="select">
    <option value="value1">Value 1</option> 
    <option value="value2" selected>Value 2</option>
    <option value="value3">Value 3</option>
    <option value="value1">Value 4</option> 
    <option value="value2">Value 5</option>
    <option value="value3">Value 6</option>
  </select>
  <hr>
  <h3>You're welcome.</h3>
</div>
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CSS 

              
                // Base styles (unimportant)
body {
  background: #7db1ff;
  color: #333;
  font: 18px/1.5 Helvetica, Arial, sans-serif;
}

.article {
  max-width: 560px;
  margin: 30px auto;
  padding: 30px 30px;
  box-sizing: border-box;
  overflow: hidden;

  
  &:before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: #fff;
    z-index: -1;
  }
}

h1 {
  margin: 0;
  padding: 0;
  font-size: 24px;
  text-align: center;
}

p {
  margin: 0 0 1em;
}

img {
  display: block;
  max-width: 100%;
}

.align-left {
  float: left;
  max-width: 35%;
  margin: 0 30px 15px 0;
}

// The magic (separated for easy of understanding)
.article {
  position: relative;
  background: #ffffff; // fallback bg for IE 8
  background: none, none; // removes fallback on newer browsers
  
  // The background color cannot be set on article or section backgrounds will be covered. I'm using the :before pseudo element instead to acheive the same result.
  &:before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: #fff;
    z-index: -1;
  }
}

hr {
  height: 0;
  margin: 30px -30px;
  border: 0;
  border-bottom: 1px solid #eee;
  position: relative;
  overflow: visible;

  // Also uses a pseudo element to set the background for each section.
  &:before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 9999em;
    background: #fff;
    z-index: -1;
  }

  &:nth-of-type(odd){
    &:before {
      background: #fafafa;
    }
  }
}
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JS
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999px

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