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HTML

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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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About the <head>

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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).

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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.

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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 

              
                <h1>You know what to do: resize your viewport!</h1>
<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. In non metus feugiat, fringilla arcu non, hendrerit magna. Duis eu ex sem. Aliquam erat volutpat. Maecenas pellentesque dui eu odio vehicula condimentum. In odio nisi, placerat sed lectus eget, interdum elementum felis. Aenean id pretium orci. Suspendisse gravida nulla eros, eu sodales diam laoreet ornare. Proin purus quam, hendrerit eu ipsum eget, gravida tincidunt justo. Praesent facilisis vel felis vel imperdiet. Phasellus dapibus magna a enim fermentum, et luctus libero mollis. Suspendisse ac varius ante, nec egestas orci. Sed sapien urna, feugiat eget congue in, varius elementum tortor.</p>
<div class="fukol">  
  <div class="fukol-grid">
    <div>1</div>
    <div>2</div>
    <div>3</div>
    <div>4</div>
    <div>5</div>
    <div>6</div>
    <div>7</div>
    <div>8</div>
    <div>9</div>
    <div>10</div>
    <div>11</div>
    <div>12</div>
  </div>
</div>
<p>Sed sem tortor, porttitor ac ultrices nec, sagittis at libero. Nulla consequat gravida erat condimentum porttitor. Nunc euismod placerat nisl, sit amet tincidunt quam rutrum non. Quisque tellus nisl, pellentesque lobortis tempus non, dictum eget magna. Duis cursus ipsum at orci condimentum faucibus. Donec placerat semper nibh eget fringilla. Mauris nisl odio, scelerisque vel metus non, ullamcorper vestibulum ipsum. Ut purus lectus, eleifend quis viverra vitae, lobortis euismod sem. Aliquam erat volutpat.</p>
!

CSS 

              
                /* The Fukol CSS 'grid system' */

.fukol-grid {
  display: flex;
  flex-wrap: wrap;
  margin: -0.5em;
}

.fukol-grid > * {
  flex: 1 0 10em;
  margin: 0.5em;
}

.fukol-grid > *:first-child {
  flex-basis: calc(100% - 1em);
}

/* Styles just for this demo */

* {
  box-sizing: border-box; /* should be covered by reset */
}

body {
  padding: 1em;
  margin: 0 auto;
  max-width: 50em;
  line-height: 1.5;
}

body * + * {
  margin-top: 1.5em;
}

.fukol-grid > * {
  background: #222;
  padding: 1em;
  color: #fff;
  text-align: center;
}
!

JS 

              
                /* haha NO */
!
999px

Console