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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

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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

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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 id="six"></div>
!

CSS 

              
                // Celebrating six years of a.singlediv.com 🎉

white(alpha)
  rgba(255,255,255,alpha)

black(alpha)
  rgba(0,0,0,alpha)

#six
  width: 130px
  height: 70px
  margin-left: -190px
  margin-top: -55px
  position: absolute
  left: 50%
  top: 50%
  background-repeat: no-repeat
  background-image: linear-gradient(160deg, alpha(midnightblue,.5), alpha(midnightblue,0) 55%),
                    repeating-linear-gradient(to right, black, black 5px, white 5px, white 10px),
                    linear-gradient(to right, alpha(midnightblue,.5) 50%, alpha(midnightblue,0) 60%),
                    linear-gradient(to left, alpha(midnightblue,0) 40%,
                                             alpha(midnightblue,.5) 50%,
                                             alpha(midnightblue,0) 60%),
                    repeating-linear-gradient(to bottom, black, black 5px, white 5px, white 10px)
  background-size: 45px 100%,
                   45px 100%,
                   70% 45px,
                   70% 45px,
                   70% 45px
  background-position: 0 0,
                       0 0,
                       0 100%,
                       100% 100%,
                       0 100%
  border-radius: 20px 0 0 20px
  box-shadow: 0 -5px 0 black,
              0 -10px 0 white,
              0 -15px 0 black,
              0 -20px 0 white,
              0 -25px 0 black,
              0 -30px 0 white,
              0 -35px 0 black,
              0 -40px 0 white,
              0 -45px 0 black

  @media (max-width: 550px)
    transform: scale(.7)
    margin-left: -152px

  &:before,
  &:after
    display: block
    content: ''
    position: absolute

  &:before
    width: 100%
    height: 100%
    top: 25px
    background-repeat: no-repeat
    background-image: linear-gradient(-160deg, alpha(midnightblue,0) 55%, alpha(midnightblue,.5)),
                      repeating-linear-gradient(to right, black, black 5px, white 5px, white 10px)
    background-size: 45px 100%
    background-position: 100% 0,
                         100% 0
    border-radius: 0 20px 20px 0
    box-shadow: 0 5px 0 black,
                0 10px 0 white,
                0 15px 0 black,
                0 20px 0 white,
                0 25px 0 black,
                0 30px 0 white,
                0 35px 0 black,
                0 40px 0 white,
                0 45px 0 black
    z-index: 2

  &:after
    width: 280px
    height: 185px
    left: 100px
    top: -45px
    background-repeat: no-repeat
    background-image: linear-gradient( 60deg, black(0) 35%,
                                              black 35.2%, black 37%,
                                              white 37.2%, white 39%,
                                              black 39.2%, black 41%,
                                              white 41.2%, white 43%,
                                              black 43.2%, black 45%,
                                              white 45.2%, white 47%,
                                              black 47.2%, black 49%,
                                              white 49.2%, white 51%,
                                              black 51.2%, black 53%,
                                              black(0) 53.2%),
                      linear-gradient(60deg, alpha(midnightblue,0) 110px, alpha(midnightblue,.5) 130px),
                      repeating-linear-gradient(to bottom, black, black 5px, white 5px, white 10px),
                      linear-gradient(to right, alpha(midnightblue,.5) 30px, alpha(midnightblue,0) 50px),
                      linear-gradient(-60deg, white 35%, white(0) 35.2%),
                      repeating-linear-gradient(to top, black, black 5px, white 5px, white 10px),
                      linear-gradient(to bottom, alpha(midnightblue,.5) 45px, alpha(midnightblue,0) 60px),
                      linear-gradient(to top, alpha(midnightblue,.5) 45px, alpha(midnightblue,0) 55px),
                      repeating-linear-gradient(to right, black, black 5px, white 5px, white 10px),
                      linear-gradient(-60deg, white(0) 53%, white 53.2%),
                      linear-gradient(60deg, alpha(midnightblue,0)  25%,
                                             alpha(midnightblue,.5) 35%,
                                             alpha(midnightblue,.5) 55%,
                                             alpha(midnightblue,0)  65%),
                      linear-gradient(to top, alpha(midnightblue,.5) 45px, alpha(midnightblue,0) 55px),
                      linear-gradient(-60deg, black(0) 35%,
                                              black 35.2%, black 37%,
                                              white 37.2%, white 39%,
                                              black 39.2%, black 41%,
                                              white 41.2%, white 43%,
                                              black 43.2%, black 45%,
                                              white 45.2%, white 47%,
                                              black 47.2%, black 49%,
                                              white 49.2%, white 51%,
                                              black 51.2%, black 53%,
                                              black(0) 53.2%)
    background-size: 200px 100%,
                     170px 45px,
                     170px 45px,
                     130px 45px,
                     200px 100%,
                     205px 45px,
                     45px 100%,
                     45px 100%,
                     45px 100%,
                     200px 100%,
                     100px 100%,
                     130px 70px,
                     200px 100%
    background-position: 115px 0,
                         0 0,
                         0 0,
                         0 100%,
                         80px 0,
                         0 100%,
                         63px 0,
                         63px 0,
                         63px 0,
                         80px 0,
                         155px 50%,
                         80px 100%,
                         80px 0
    z-index: 1

body
  height: 100vh
  width: 100vw
  position: relative
  background-color: white
!

JS
!
999px

Console