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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-.

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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 

              
                
<html><head></head><body>
  <div style="margin: 5% auto; width:80%;">
    <div id="errorMessage">
      <h3>It appears that your browser doesn't support webkit CSS Regions.</h3>
      <p>To view this demo:</p>
      <ol>
        <li>Download <a href="https://www.google.com/intl/en/chrome/browser/canary.html">Chrome Canary</a> on Desktop or <a href="https://play.google.com/store/apps/details?id=com.chrome.beta&amp;hl=en">Chrome Beta</a> on Android.</li>
        <li>Navigate in the address bar to <code style="font-weight: bold;">about://flags</code>.</li>
        <li>Enable <code>Experimental WebKit Features</code>.</li>
      </ol>
      <h3>ご利用のブラウザはWebkitのCSSリージョンが未対応のようです。</h3>
      <p>本デモを見るには：</p>
      <ol>
        <li>デスクトップ用の <a href="https://www.google.com/intl/ja/chrome/browser/canary.html">Chrome Canary</a> またはAndroid用の <a href="https://play.google.com/store/apps/details?id=com.chrome.beta&amp;hl=en">Chrome Beta</a> をダウンしてください。</li>
        <li>アドレスバーに <code style="font-weight: bold;">about://flags</code> を入力し、アクセスしてください。</li>
        <li>設定項目の <code>試験運用版のWebKit機能</code> を有効にしてください。</li>
      </ol>
    </div>
    <div id="errorRegion"></div>
    <div id="regionA"></div>
    <div id="regionA"></div>
  </div>
  
  <div id="contentA">
    <div id="circle"></div>
    <div id="circle-paint"></div>
    <p>On a gentle slope above a trail junction in Sequoia National Park, about 7,000 feet above sea level in the southern Sierra Nevada, looms a very big tree. Its trunk is rusty red, thickened with deep layers of furrowed bark, and 27 feet in diameter at the base. Its footprint would cover your dining room. Trying to glimpse its tippy top, or craning to see the shape of its crown, could give you a sore neck. That is, this tree is so big you can scarcely look at it all. It has a name, the President, bestowed about 90 years ago by admiring humans. It's a giant sequoia, a member of Sequoiadendron giganteum, one of several surviving species of redwoods.</p>
    <div id="rect"></div>
    <div id="rect-paint"></div>
    <p>It's not quite the largest tree on Earth. It's the second largest. Recent research by scientist Steve Sillett of Humboldt State University and his colleagues has confirmed that the President ranks number two among all big trees that have ever been measured - and Sillett's team has measured quite a few. It doesn't stand so tall as the tallest of coast redwoods or of Eucalyptus regnans in Australia, but height isn't everything; it's far more massive than any coast redwood or eucalypt. Its dead spire, blasted by lightning, rises to 247 feet. Its four great limbs, each as big as a sizable tree, elbow outward from the trunk around halfway up, billowing into a thick crown like a mushroom cloud flattening against the sky. Although its trunk isn't quite so bulky as that of the largest giant, the General Sherman, its crown is fuller than the Sherman's. The President holds nearly two billion leaves.</p>
    
    <p>Trees grow tall and wide-crowned as a measure of competition with other trees, racing upward, reaching outward for sunlight and water. And a tree doesn't stop getting larger - as a terrestrial mammal does, or a bird, their size constrained by gravity - once it's sexually mature. A tree too is constrained by gravity, but not in the same way as a condor or a giraffe. It doesn't need to locomote, and it fortifies its structure by continually adding more wood. Given the constant imperative of seeking resources from the sky and the soil, and with sufficient time, a tree can become huge and then keep growing. Giant sequoias are gigantic because they are very, very old.</p>
    <p>They are so old because they have survived all the threats that could have killed them. They're too strong to be knocked over by wind. Their heartwood and bark are infused with tannic acids and other chemicals that protect against fungal rot. Wood-boring beetles hardly faze them. Their thick bark is flame resistant. Ground fires, in fact, are good for sequoia populations, burning away competitors, opening sequoia cones, allowing sequoia seedlings to get started amid the sunlight and nurturing ash. Lightning hurts the big adults but usually doesn't kill them. So they grow older and bigger across the millennia.</p>
    <p>Another factor that can end the lives of big trees, of course, is logging. Many giant sequoias fell to the ax during the late 19th and early 20th centuries. But the wood of the old giants was so brittle that trunks often shattered when they hit the ground, and what remained had little value as lumber. It went into shingles, fence posts, grape stakes, and other scrappy products. Given the difficulties of dealing with logs 20 feet thick, broken or unbroken, the trees were hardly worth cutting. Sequoia National Park was established in 1890, and automobile tourism soon showed that giant sequoias were worth more alive.</p>
  </div>
  </body>
</html>
!

CSS 

              
                #contentA {
  -webkit-flow-into: a;
  font-size: 14px;
  text-align: justify;
}
#regionA {
  -webkit-flow-from: a;
  background-color: #fff0f0;
  width: 45%;
  padding: 1%;
  margin-right: 2%;
  height: 400px;
  float: left;
  overflow: hidden;
}
#container {
  width: 500px;
  margin: 50px auto;
  background-color: #fee;
}
#circle {
  float: right;
  -webkit-shape-outside: circle(0, 0, 100px);
  -webkit-shape-margin: 5px;
}
#circle-paint {
  position: absolute;
  right: 0px;
  margin-top: 5px;
  border-radius: 50%;
  width: 200px;
  height: 200px;
  background-color: #88f;
}
#rect {
  float: left;
  -webkit-shape-outside: polygon(100px 0, 200px 100px, 100px 200px, 0 100px);
  -webkit-shape-margin: 5px;
}
#rect-paint {
  -webkit-transform: rotate(45deg);
  position: absolute;
  left: 25px;
  margin-top: 35px;
  border-radius: 5%;
  width: 141px;
  height: 141px;
  background-color: #88f;
}

#errorMessage {
  -webkit-flow-into: err;
  background-color: #fcc;
  padding: 1em;
}
#errorRegion {
  -webkit-flow-from: err;
  display: none;
}
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JS
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999px

Console