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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>

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).

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JavaScript

About JavaScript Preprocessors

JavaScript preprocessors can help make authoring JavaScript easier and more convenient. For instance, CoffeeScript can help prevent easy-to-make mistakes and offer a cleaner syntax and Babel can bring ECMAScript 6 features to browsers that only support ECMAScript 5.

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Babel is required to process package imports. If you need a different preprocessor remove all packages first.

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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HTML 

              
                <header>
  <h1>This is my awesome title</h1>
</header>
<div id="main">
  <article>
    <h1>Main</h1>
    <p>Leave dead animals as gifts unwrap toilet paper<p>
    
    <p>Use lap as chair eat grass, throw it back up yet destroy the blinds but wake up human for food at 4am so meow my left donut is missing, as is my right, favor packaging over toy. The dog smells bad caticus cuteicus for claw drapes meow for human give me attention meow sit in box stare at ceiling. Find something else more interesting human give me attention meow. Eat from dog's food refuse to leave cardboard box. Scratch the furniture hide head under blanket so no one can see and sleep in the bathroom sink destroy couch as revenge scratch the furniture sweet beast, for have secret plans. Eat grass, throw it back up get video posted to internet for chasing red dot but eat and than sleep on your face. Sweet beast i like big cats and i can not lie, or loves cheeseburgers get video posted to internet for chasing red dot swat at dog, for cat slap dog in face but burrow under covers. Instantly break out into full speed gallop across the house for no reason the dog smells bad lick arm hair. Chase red laser dot lounge in doorway or under the bed. Kitty loves pigs hide head under blanket so no one can see. Swat at dog chase laser hiss at vacuum cleaner lounge in doorway behind the couch, or lick arm hair stretch. Sleep in the bathroom sink hopped up on catnip then cats take over the world for have secret plans vommit food and eat it again.</p>


  </article>
  <nav>
    <h1>Nav</h1>
  </nav>
  <aside>
    <h1>Sidebar</h1>
  </aside>
</div>
<footer>
  <h1>Footer content</h1>
</footer>
!

CSS 

              
                body {
  padding: 2vw;
}

#main { 
  display: flex;
}

header, 
footer,
#main > article,
#main > nav,
#main > aside {
  border: 1px solid red;
  padding: 2vw;
}

#main > article { 
  order: 2; 
  min-width: 12em; 
  flex:1;
}
#main > nav { 
  order: 1; 
  width: 200px; 
}

#main > aside {
  order: 3; 
  width: 200px;
}

article p:first-of-type {
  font-size: 1.25em;
  font-style: italic;
}

@media all and (max-width: 800px) {
  /* 
    Too narrow to support three columns 
  */
  #main {
    flex-flow: column;
  }
  
  #main > article, 
  #main > nav, 
  #main > aside {
    /* Return them to document order */
    order: 0;
    padding: 5vw;
    width: auto;
  }
}
!

JS
!
999px

Console