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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

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.

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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.

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.

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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.

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

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HTML 

              
                <div></div>
!

CSS 

              
                div {
  /*border: double;
  border-width: 180px;
  border-color: red transparent blue yellow;
  border-radius: 220px;
  height: 10px;
  width: 120px;
  -webkit-box-reflect: below -100px;*/
  height: 500px;
  width: 280px;
  margin: auto;
  background: #f3c957;
  background-image: 
    radial-gradient(circle at 155px 120px, white 3px, transparent 15px), 
    radial-gradient(circle at 171px 145px, white 1px, transparent 11px), 
    radial-gradient(ellipse farthest-side at 171px 275px, black 5px, #f3c957 8px, #f3c957 10px, transparent 13px), 
    radial-gradient(ellipse farthest-side at 168px 285px, #d79e26 5px, #f3c957 10px, transparent 14px), 
    radial-gradient(circle at 140px 140px, black 5px, black 10px, red 27px, red 31px, brown 38px, black 40px, black 41px, rgba(243, 201, 87, 1) 41px, rgba(243, 201, 87, 1) 71px, #564841 71px, #ffffff 85px, #ffffff 90px, #b7c0d6 100px, transparent 100px), 
    linear-gradient(to bottom, #f3c957 110px, #1c1916 110px, #7c7d81 140px, #1c1916 170px, #d79e26 170px, #d79e26 177px, transparent 180px, transparent 330px, transparent 350px, transparent 410px, blue 410px), 
    radial-gradient(circle at 70px 340px, grey 5px, black 5px, black 15px, transparent 15px), 
    radial-gradient(circle at 215px 340px, grey 5px, black 5px, black 15px, transparent 15px), 
    radial-gradient(circle at 0px 360px, transparent 40px, transparent 57px, blue 65px, blue 90px, transparent 96px), 
    radial-gradient(circle at 285px 360px, transparent 40px, transparent 57px, blue 65px, blue 90px, transparent 97px), 
    radial-gradient(circle at 140px 150px, #d79e26 90px, #d79e26 100px, #f3c957 105px, #f3c957 165px, transparent 177px), 
    radial-gradient(ellipse closest-side at 145px 105px, #f3c957 220px, #f3c957 270px, black 270px, transparent 271px), 
    radial-gradient(circle at 145px 240px, transparent 110px, #04049a 110px, #04049a 112px, transparent 113px), 
    linear-gradient(to right, transparent 35px, blue 35px, blue 140px, blue 250px, transparent 170px, transparent 350px, blue 350px);
  border-radius: 500px / 90% 90% 50% 50%;
  box-shadow: 0 0 50px 5px rgba(215, 158, 38, .61) inset;
}

div:after {
  content: "\0000a0vv\0000a0";
  color: #f3c957;
  font-size: 420px;
  font-family: 'Orbitron', sans-serif;
  line-height: 30px;
  width: 190px;
  height: 80px;
  background-color: transparent;
  position: relative;
  z-index: -99999;
  left: -515px;
  top: 275px;
  border-radius: 5px / 90% 90% 50% 50%;
  background-image: radial-gradient(ellipse farthest-side at 130px 135px, #29293d 5%, transparent 5%), radial-gradient(ellipse farthest-side at 130px 137px, darkgrey 5%, transparent 5%), radial-gradient(circle closest-side at 160px 140px, #29293d 9%, transparent 9%), radial-gradient(circle closest-side at 160px 141px, darkgrey 9%, transparent 9%), radial-gradient(ellipse farthest-corner at 140px 150px, black 4%, transparent 4%), radial-gradient(ellipse farthest-side at 527px 135px, #29293d 5%, transparent 5%), radial-gradient(ellipse farthest-side at 527px 137px, darkgrey 5%, transparent 5%), radial-gradient(circle closest-side at 496px 140px, #29293d 9%, transparent 9%), radial-gradient(circle closest-side at 496px 141px, darkgrey 9%, transparent 9%), radial-gradient(ellipse farthest-corner at 515px 150px, black 4%, transparent 4%);
}

div:before {
  content: "k\0000a0";
  color: blue;
  font-size: 420px;
  font-family: 'Orbitron', sans-serif;
  line-height: 30px;
  width: 290px;
  height: 80px;
  background-color: transparent;
  position: relative;
  z-index: -99999;
  left: 40px;
  top: 385px;
  background-image: radial-gradient(ellipse farthest-corner at 47px 385px, black 5%, transparent 5%), radial-gradient(circle at 181px 390px, black 5%, transparent 5%), radial-gradient(circle at 204px 394px, black 4%, transparent 4%);
}
!

JS
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999px

Console