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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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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).

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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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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 

              
                <input hidden aria-hidden="true" type="checkbox" name="toggle-nav" id="toggle-id"/>
<aside>
  <header role="banner">
    <nav>
      <label for="toggle-id">
        <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 20 20">
          <path d="M2,2L18,18M18,2L2,18"/>
        </svg>
        Close Menu
      </label>
    </nav>
  </header>
  <ul>
    <li><a href="#">Option</a></li>
    <li><a href="#">Stuff</a></li>
    <li><a href="#">Nonsense</a></li>
    <li><a href="#">About</a></li>
    <li><a href="#">Help</a></li>
  </ul>
</aside>
<main>
  <header role="banner">
    <nav>
      <label for="toggle-id">
        <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 20 20">
          <path d="M2,2l16,0m-16,8l16,0m-16,8l16,0"/>
        </svg>
        Menu
      </label>
      <b>Logo</b>
    </nav>
  </header>
  <article>
    <h1>The main title</h1>
    <p>Sometimes you don't even need JavaScript to do the core interactive functionality of your website. Sometimes just CSS is more than enough, when you understand how it really works.</p>
    <p>For more details about this feel free to read the accompanying post on <a href="http://darksnow.net/code/off-canvas-without-javascript">my blog</a>.</p>
  </article>
</main>
!

CSS 

              
                $menu-width: 200px;

body {
  font-family: -apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,"Helvetica Neue",Arial,sans-serif;
  font-size: 1rem;
  line-height: 1.618em;
}

html, body, main {
  height: 100%;
}

aside {
  position: fixed;
  height: 100%;
  z-index: 1;
  background: #333;
  width: $menu-width;
  overflow-x: hidden;
}

main {
  z-index: 2;
  background: white;
  position: fixed;
  transition: transform 1s;
  overflow-y: auto;
}
article {
  padding: 1em;
}

header {
  background: #39f;
  padding: 0.5em 1em;
}
nav {
  display: flex;
  b {
    flex-grow: 1;
    text-align: right;
  }
}
svg {
  height: 1em;
  vertical-align: middle;
}
path {
  stroke: black;
  stroke-width: 3;
}
h1 {
  font-size: 2em;
  font-weight: bold;
}
p {
  margin-top: 1em;
}
a {
  color: #ff8133;
  font-weight: bold;
  text-decoration: none;
}
ul {
  padding: 1em;
}
/* Since all labels for the for attribute are
 * clickable, make them look like they are. */
label[for] {
  cursor: pointer;
}
/* Make sure the hidden checkbox is really hidden
 * from all consumers of this content. */
input[hidden] {
  display: none;
  &:checked ~ main {
    transform: translateX($menu-width);
  }
}
!

JS
!
999px

Console