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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>

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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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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.

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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>Adaptive design</h1>
<article>
  <p>When media queries arrived in CSS it opened the door to making layouts more flexible. But developers were still most comfortable making fixed-width layouts. One technique involved switching between a handful of fixed-width layouts at specified widths.</p>
  <p>This allowed designers to provide layouts that looked good at a few different sizes but the design never looked quite right when viewed <em>between</em> those sizes. The problem of excess space persisted although it wasn’t as bad as in a fixed-width layout.</p>
</article>
<aside>
  <p>Ultimately this technique wasn’t very popular. The term “adaptive” was also used to refer to other approaches so it can be a confusing descriptor for what was quite a niche technique.</p>
  <p>This example is using the CSS <code>float</code> property to create columns. That was a popular technique before CSS grid or flexbox existed.</p>
</aside>
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CSS 

              
                body {
  font-family: sans-serif;
  line-height: 1.5;
  padding: 0 16px;
}

h1 {
  margin-bottom: 0;
}

@media all and (min-width: 800px) {
  article {
    width: 540px;
    float: left;
  }
  
  aside {
    width: 250px;
    float: left;
    margin-left: 10px;
  }
}

@media all and (min-width: 1200px) {
  article {
    width: 800px;
    float: left;
  }
  
  aside {
    width: 350px;
    float: left;
    margin-left: 50px;
  }
}

@media all and (min-width: 1600px) {
  h1 {
    width: 400px;
    float: left;
  }
  
  article {
    width: 800px;
    float: left;
  }
  
  aside {
    width: 350px;
    float: left;
    margin-left: 50px;
  }
}
!

JS
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999px

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