Pen Settings

HTML

About HTML Preprocessors

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.

Learn more · Versions

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.

!
Insecure Resource

The resource you are linking to is using the 'http' protocol, which may not work when the browser is using https.

CSS

About CSS Preprocessors

CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.

Learn more · Versions

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

Any URLs added here will be added as <link>s in order, and before the CSS in the editor. You can use the CSS from another Pen by using its URL and the proper URL extension.

Powered by Algolia
About External Resources

You can apply CSS to your Pen from any stylesheet on the web. Just put a URL to it here and we'll apply it, in the order you have them, before the CSS in the Pen itself.

You can also link to another Pen here (use the .css URL Extension) and we'll pull the CSS from that Pen and include it. If it's using a matching preprocessor, use the appropriate URL Extension and we'll combine the code before preprocessing, so you can use the linked Pen as a true dependency.

Learn more

+ add another resource

JavaScript

About JavaScript Preprocessors

JavaScript preprocessors can help make authoring JavaScript easier and more convenient.

Learn more · Versions

Babel includes JSX processing.

Add External Scripts/Pens

Any URL's added here will be added as <script>s in order, and run before the JavaScript in the editor. You can use the URL of any other Pen and it will include the JavaScript from that Pen.

Powered by Algolia
About External Resources

You can apply a script from anywhere on the web to your Pen. Just put a URL to it here and we'll add it, in the order you have them, before the JavaScript in the Pen itself.

If the script you link to has the file extension of a preprocessor, we'll attempt to process it before applying.

You can also link to another Pen here, and we'll pull the JavaScript from that Pen and include it. If it's using a matching preprocessor, we'll combine the code before preprocessing, so you can use the linked Pen as a true dependency.

Learn more

+ add another resource

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.

Powered by Algolia
About Packages

Using packages here is powered by Skypack, which makes packages from npm not only available on a CDN, but prepares them for native JavaScript ES6 import usage.

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

If you're using React / ReactDOM, make sure to turn on Babel for the JSX processing.

Behavior

Save Automatically?

If active, Pens will autosave every 30 seconds after being saved once.

Auto-Updating Preview

If enabled, the preview panel updates automatically as you code. If disabled, use the "Run" button to update.

Format on Save

If enabled, your code will be formatted when you actively save your Pen. Note: your code becomes un-folded during formatting.

Editor Settings

Code Indentation

Want to change your Syntax Highlighting theme, Fonts and more?

Visit your global Editor Settings.

HTML 

              
                <div window>
  <div class="main">
    <h1>Fruits</h1>
    <details>
      <summary>Apple</summary>
      <div class="detail-body">
        <p>
          Lorem Ipsum is simply dummy text of the 
          printing and typesetting industry. Lorem 
          Ipsum has been the industry's standard dummy 
          text ever since the 1500s, when an unknown 
          printer took a galley of type and scrambled 
          it to make a type specimen book. It has survived 
          not only five centuries, but also the leap into 
          electronic typesetting, remaining essentially 
          unchanged. 
       </p>
      </div>
    </details>
    <details>
      <summary>Banana</summary>
      <div class="detail-body">
        <p>
          The standard chunk of Lorem Ipsum used since 
          the 1500s is reproduced below for those interested.
          Sections 1.10.32 and 1.10.33 from "de Finibus Bonorum 
          et Malorum" by Cicero are also reproduced in their 
          exact original form, accompanied by English versions 
          from the 1914 translation by H. Rackham. The first line 
          of Lorem Ipsum, "Lorem ipsum dolor sit amet..", 
          comes from a line in section 1.10.32.
        </p>
      </div>
    </details>
    <details>
      <summary>Pear</summary>
      <div class="detail-body">
        <p>
          It is a long established fact that a reader will be 
          distracted by the readable content of a page when 
          looking at its layout. The point of using Lorem 
          Ipsum is that it has a more-or-less normal 
          distribution of letters, as opposed to using 
          Content here, content here', making it look like 
          readable English. Many desktop publishing packages 
          and web page editors now use Lorem Ipsum as their  
          default model text, and a search for 'lorem ipsum' 
          will uncover many web sites still in their infancy.
        </p>
      </div>
    </details>
    <details>
      <summary>Orange</summary>
      <div class="detail-body">
        <p>
          Contrary to popular belief, Lorem Ipsum is not 
          simply random text. It has roots in a piece of 
          classical Latin literature from 45 BC, making 
          it over 2000 years old. Richard McClintock, 
          a Latin professor at Hampden-Sydney College 
          in Virginia, looked up one of the more obscure 
          Latin words, consectetur.
        </p>
      </div>
    </details>
  </div>
</div>
!

CSS 

              
                :root {
  --w: 20em; 
  --easing: cubic-bezier(0.165, 0.84, 0.44, 1);
}

@media screen and (max-height: 35em) {
  :root {
    --w: 50vh;  
  }  
}

html, body {
  height: 100%;
  min-height: 100%;
  margin: 0;
}

body {
  display: flex;
  align-items: center;
  justify-content: center;
  background: #f0f0f0;
}

[window] {
  width: var(--w);
  height: calc(var(--w) *1.6);
  min-width: 15em;
  min-height: 20em;
  position: relative;

  /* just for demo */
  background: #444;
  box-shadow: 0 0 20px rgba(125, 125, 125, .2);
  overflow: hidden;
}

@keyframes slide-in {
  0% { transform: translate3d(10%, 10%, 0); }
  100% { transform: translate3d(1em, 1em, 0); }
}

@keyframes clip-in {
  from {
    transform: translate3d(1em, 100%, 0);
    -webkit-clip-path: polygon(0 0, -10% 0, -10% 100%, 0 100%);
            clip-path: polygon(0 0, -10% 0, -10% 100%, 0 100%);
  }
  to {
    transform: translate3d(0, 0, 0);
    -webkit-clip-path: polygon(0 0, 100% 0, 98% 100%, 0 100%);
            clip-path: polygon(0 0, 100% 0, 98% 100%, 0 100%);
  }
}

.main {
  z-index: 9;
  display: flex;
  justify-content: center;
  flex-direction: column;
  align-items: center;
  width: 100%; height: 100%;
  background: #fff;
  transition: .4s var(--easing); 
}

.main h1 {
  margin: -2em 0 1em 0;
  min-width: 68%;
}

.main[open] {
  transform: scale(.9) translate3d(-.5em, -.5em, 0);
}

.main details {
  display: block;
  width: 68%;
}

.main details + details {
  margin-top: 5px;
}

.main details summary {
  padding: .5em 1em;
  background: #fafafa;
  color: #333;
  cursor: pointer;
  transition: .4s var(--easing); 
  outline: none;
}

.main details:not([open]) summary:focus {
  box-shadow: inset 0 0 0 1px #9bdeff;
  color: #000;
}

.main details summary::-webkit-details-marker {
  opacity: .5;
}

.main details:not([open]):hover summary::-webkit-details-marker,
.main details:not([open]) summary:focus::-webkit-details-marker,
.main details[open] summary::-webkit-details-marker {
  opacity: 1;
}

.main details:not([open]):hover summary {
  background: #E3F5FE;
  color: #000;
}

.main details[open] summary {
  background: #E3F5FE;
  animation: clip-in .3s;
  animation-fill-mode: both;
  min-width: 61.8%;
  will-change: transform;
}

.main details summary ~ .detail-body {
  display: flex;
  flex-direction: column;
  padding: 4em 2em 2em;
  background: #fff;
  position: absolute;
  top: 0; bottom: 0; left: 0; right: 0;
  box-shadow: 0 0 20px rgba(125, 125, 125, .5);
  animation: slide-in .6s var(--easing); 
  animation-fill-mode: both;
  will-change: transform;
  z-index: 10;
  overflow: auto;
}

.main details summary ~ .detail-body p {
  line-height: 1.6;
  margin-top: 2em;
}

.main details[open] summary {
  position: absolute;
  z-index: 99;
  top: 1em;
  left: 1em;
}
!

JS 

              
                const main = document.querySelector('.main');
main && main.addEventListener('click', function(e) {
  if (e.target.tagName.toLowerCase() == 'summary') {
    if (e.target.parentNode.open) {
      main.removeAttribute('open');
    } else {
      main.setAttribute('open', true);
    }
  }
});
!
999px

Console