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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.

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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

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.

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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.

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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.

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.

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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.

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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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About Packages

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="css-slideshow">
	<figure>
		<img src="http://themarklee.com/wp-content/uploads/2013/10/class-header-css3.jpg" alt="class-header-css3" width="495" height="370" class="alignnone size-full wp-image-172" /><figcaption><strong>CSS3:</strong> CSS3 delivers a wide range of stylization and effects, enhancing the web app without sacrificing your semantic structure or performance. Additionally Web Open Font Format (WOFF) provides typographic flexibility and control far beyond anything the web has offered before.</figcaption> 
	</figure>
	<figure>
		<img src="http://themarklee.com/wp-content/uploads/2013/10/class-header-semantics.jpg" alt="class-header-semantics" width="495" height="370" class="alignnone size-full wp-image-179" /><figcaption><strong>Semantics:</strong> Giving meaning to structure, semantics are front and center with HTML5. A richer set of tags, along with RDFa, microdata, and microformats, are enabling a more useful, data driven web for both programs and your users.</figcaption> 
	</figure>
	<figure>
		<img src="http://themarklee.com/wp-content/uploads/2013/10/class-header-offline.jpg" alt="class-header-offline" width="495" height="370" class="alignnone size-large wp-image-178" /><figcaption><strong>Offline &amp; Storage:</strong> Web Apps can start faster and work even if there is no internet connection, thanks to the HTML5 App Cache, as well as the Local Storage, Indexed DB, and the File API specifications.</figcaption> 
	</figure>
	<figure>
		<img src="http://themarklee.com/wp-content/uploads/2013/10/class-header-device.jpg" alt="class-header-device" width="495" height="370" class="alignnone size-full wp-image-177" /><figcaption><strong>Device Access:</strong> Beginning with the Geolocation API, Web Applications can present rich, device-aware features and experiences. Incredible device access innovations are being developed and implemented, from audio/video input access to microphones and cameras, to local data such as contacts &amp; events, and even tilt orientation.</figcaption> 
	</figure>
<figure>
		<img src="http://themarklee.com/wp-content/uploads/2013/10/class-header-connectivity.jpg" alt="class-header-connectivity" width="495" height="370" class="alignnone size-large wp-image-176" /><figcaption><strong>Connectivity:</strong> More efficient connectivity means more real-time chats, faster games, and better communication. Web Sockets and Server-Sent Events are pushing (pun intended) data between client and server more efficiently than ever before.</figcaption> 
	</figure>
	<figure>
		<img src="http://themarklee.com/wp-content/uploads/2013/10/class-header-multimedia.jpg" alt="class-header-multimedia" width="495" height="370" class="alignnone size-large wp-image-175" /><figcaption><strong>Multimedia:</strong> Audio and video are first class citizens in the HTML5 web, living in harmony with your apps and sites. Lights, camera, action!</figcaption> 
	</figure>
	<figure>
		<img src="http://themarklee.com/wp-content/uploads/2013/10/class-header-3d.jpg" alt="class-header-3d" width="495" height="370" class="alignnone size-large wp-image-174" /><figcaption><strong>3D, Graphics &amp; Effects:</strong> Between SVG, Canvas, WebGL, and CSS3 3D features, you're sure to amaze your users with stunning visuals natively rendered in the browser.</figcaption> 
	</figure>
	<figure>
		<img src="http://themarklee.com/wp-content/uploads/2013/10/class-header-performance.jpg" alt="class-header-performance" width="495" height="370" class="alignnone size-large wp-image-173" /><figcaption><strong>Performance &amp; Integration:</strong> Make your Web Apps and dynamic web content faster with a variety of techniques and technologies such as Web Workers and XMLHttpRequest 2. No user should ever wait on your watch.</figcaption> 
	</figure>
  </div>  
<p class="css-slideshow-attr"><a href="http://www.w3.org/html/logo/" target="_top">Images and captions are from the W3C</a></p>
!

CSS 

              
                body{
font-family: "HelveticaNeue-Light", "Helvetica Neue Light", "Helvetica Neue", Helvetica, Arial, "Lucida Grande", sans-serif; 
  font-weight: 300;
}
.css-slideshow{
  position: relative;
  max-width: 495px;
  height: 370px;
  margin: 5em auto .5em auto;
}
.css-slideshow figure{
  margin: 0;
  max-width: 495px;
  height: 370px;
  background: #000;
  position: absolute;
}
.css-slideshow img{
  box-shadow: 0 0 2px #666;
}
.css-slideshow figcaption{
  position: absolute;
  top: 0;
  color: #fff;
  background: rgba(0,0,0, .3);
  font-size: .8em;
  padding: 8px 12px;
  opacity: 0;
  transition: opacity .5s;
}
.css-slideshow:hover figure figcaption{
  transition: opacity .5s;
  opacity: 1;
}
.css-slideshow-attr{
  max-width: 495px;
  text-align: right;
  font-size: .7em;
  font-style: italic;
  margin:0 auto;
}
.css-slideshow-attr a{
  color: #666;
}
.css-slideshow figure{
  opacity:0;
}
figure:nth-child(1) {
  animation: xfade 48s 42s infinite;
}
figure:nth-child(2) {
  animation: xfade 48s 36s infinite;
}
figure:nth-child(3) {
  animation: xfade 48s 30s infinite;
}
figure:nth-child(4) {
  animation: xfade 48s 24s infinite;
}
figure:nth-child(5) {
  animation: xfade 48s 18s infinite;
}
figure:nth-child(6) {
  animation: xfade 48s 12s infinite;
}
figure:nth-child(7) {
  animation: xfade 48s 6s infinite;
}
figure:nth-child(8) {
  animation: xfade 48s 0s infinite;
}

@keyframes xfade{
  0%{
    opacity: 1;
  }
  10.5% {
    opacity: 1;
  }
  12.5%{
    opacity: 0;
  }
  98% {
    opacity: 0;
  }
  100% {
    opacity: 1;
  }
}
!

JS 

              
                //
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999px

Console