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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

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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.

Add External Scripts/Pens

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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 

              
                .card
  %h1
    Luke Skywalker
  %img{src: "http://static.wix.com/media/9173d6_b6e7d7a2d6e92e1a1da9aefda77fa7d7.jpg_256"}
  %p.bio
    Luke Skywalker was the son of Anakin Skywalker and Padmé Amidala, and the older twin brother of Leia Organa Solo. He was a Jedi Master and hero of the Galactic Civil War. A celebrated pilot and leader, Skywalker was most famous for destroying the first Death Star and prompting Darth Vader to kill Emperor Palpatine, which led to the eventual downfall of the Galactic Empire.

.comment
  If you didn't catch the animation, hit Cmd + Shift + 5 or refresh the page :)
!

CSS 

              
                @import compass

@import url(https://fonts.googleapis.com/css?family=Roboto+Slab)
@import url(https://fonts.googleapis.com/css?family=Merriweather+Sans:300)

*
  box-sizing: border-box

body
  background-color: #2C2D3D

.card
  width: 600px
  margin: 40px auto
  background-color: #F7F7E9
  color: #444
  overflow: hidden // clearfix
  box-shadow: 5px 5px 0 0 #aaa
  
  h1
    margin: 0
    padding: 20px
    text-align: center
    font:
      family: Roboto Slab
      weight: 400
    background-color: #4DD65F
    animation: fadein 1.2s
    
  img
    float: left
    width: 200px
    height: 200px
    margin: 20px
    position: relative
    z-index: 1
    animation: grow 0.6s
    
  .bio
    position: relative
    margin: 20px
    font-family: Merriweather Sans
    animation: slidein 1.2s
      
@keyframes fadein
  from
    color: hsla(0, 0, 0, 0)
  to
    color: inherit

@keyframes grow
  from
    transform: scale(0)
  80%
    transform: scale(1.1)
  to
    transform: scale(1)

@keyframes slidein
  from
    opacity: 0
  49.9%
    opacity: 0
  50%
    left: -240px
  to
    left: 0

.comment
  font:
    family: Merriweather Sans
    size: 12px
  color: #ddd
  text-align: center
!

JS
!
999px

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