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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

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

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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 

              
                nav
  .logo
  ul
    li
      a(href="#") Item 1
    li
      a(href="#") Item 2
    li
      a(href="#") Item 3
    li
      a(href="#") Item 4
header
  .headline
    .inner
      h1 Hello
      p Scroll down the page
section
  h2 Lorem ipsum
  p Sed lectus mi, eleifend quis congue non, lacinia id quam. Cras porta pellentesque nulla, ac auctor ligula scelerisque non. In vel placerat lacus. Nam pretium vitae purus et laoreet. Aliquam erat volutpat. Pellentesque id volutpat sem, et condimentum nisl. Donec bibendum congue mauris, ac commodo tortor volutpat ac. Donec lobortis lorem nisi, sit amet bibendum lacus vestibulum interdum. Donec mollis ligula at semper iaculis.
  p Duis et vestibulum turpis. Duis non ultrices quam. Sed volutpat imperdiet sollicitudin. Aliquam erat volutpat. Donec at adipiscing purus. Duis varius metus vitae mattis pellentesque. Etiam tempor urna sed congue vulputate. Nulla neque metus, vulputate a dui ut, suscipit fringilla risus. Suspendisse posuere dignissim vestibulum. Praesent congue vestibulum dolor, quis lobortis libero egestas ac. Sed venenatis bibendum interdum. Curabitur rhoncus urna quis viverra varius. Cras posuere non tortor at volutpat. Suspendisse porta, turpis at ullamcorper imperdiet, felis lacus eleifend sapien, pulvinar elementum ipsum lacus ut elit. Sed ipsum erat, porttitor non malesuada at, interdum at nibh. Mauris ut ornare purus.

  h2 Nulla vitae lacus
  p Praesent commodo elit vel massa gravida lacinia. Maecenas auctor dignissim porttitor. Donec tincidunt mi eget semper bibendum. Morbi quis sagittis sapien. Fusce ut ligula purus. Nulla tristique augue nec lectus lacinia congue. Nunc tempus eros quam, ac sollicitudin mauris vehicula ac. Vivamus pulvinar elit ac risus placerat rutrum.
  p Magna indoctum erroribus no his, alii fabellas eum an. Et tota clita eleifend eum, pri ne euismod eloquentiam, sea ei quas tibique. Ipsum tamquam cum id, tota clita congue ad usu. Ex eos admodum nominati. Eam ei summo dictas nostrum, vim harum graeco apeirian te. Sensibus persequeris nam an, cu legere oblique tincidunt eos, et soleat vivendum indoctum eos.
  p Donec lobortis porta ipsum a tristique. Integer sit amet ipsum porta, bibendum mauris vitae, ultricies lectus.
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CSS 

              
                @import url(https://fonts.googleapis.com/css?family=Open+Sans:300,400,700);

body {
  margin: 0;
  padding: 0;
  font-family: 'Open Sans', sans-serif;
  color: #333;
}

header {
  background: #111;
}

.headline {
  position: relative;
  height: 400px;
  color: #fff;
  text-align: center;
  background: url('https://farm9.staticflickr.com/8088/8363737128_b76782c7a2_b.jpg') no-repeat center center;
  background-size: cover;
  &:after {
    position: absolute;
    content: '';
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(#111, 0.5);
  }
}

.inner {
  position: absolute;
  top: 50%;
  left: 50%;
  opacity: 0;
  z-index: 10;
  transform: translateX(-50%) translateY(-50%);
  animation: fade-in 0.75s 0.25s ease-in forwards;
  h1 {
    margin: 0;
    font-size: 4em;
    line-height: 1.2em;
  }
  p {
    margin: 0;
    font-size: 1.4em;
    font-style: italic;
    font-family: serif;
  }
}

nav {
  position: fixed;
  width: 100%;
  z-index: 10;
  &.scrolled {
    background: rgba(#111, 0.9);
  }
  ul {
    float: right;
    list-style: none;
    padding: 25px;
    margin: 0;
  }
  li {
    float: left;
  }
  a {
    font-size: 0.9em;
    color: #fff;
    text-decoration: none;
    margin: 5px 0 0 20px;
    display: block;
    &:hover {
      color: darken(#fff, 7%);
    }
  }
}

.logo {
  height: 75px;
  float: left;
  &:before, &:after {
    position: absolute;
    font-size: 7em;
    font-weight: 300;
    line-height: 0;
    color: #fff;
    top: 25px;
  }
  &:before {
    content: '\00BB';
    left: 20px;
  }
  &:after {
    content: '\00AB';
    left: 34px;
  }
}

section {
  width: 100%;
  margin: 25px auto;
  padding: 20px;
  max-width: 800px;
  font-size: 1.2em;
  line-height: 1.6em;
  box-sizing: border-box;
}

@keyframes fade-in {
  0% {
    opacity: 0;
  }
  100% {
    opacity: 1;
  }
}
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JS 

              
                var $headline = $('.headline'),
    $inner = $('.inner'),
    $nav = $('nav'),
    navHeight = 75;

$(window).scroll(function() {
  var scrollTop = $(this).scrollTop(),
      headlineHeight = $headline.outerHeight() - navHeight,
      navOffset = $nav.offset().top;

  $headline.css({
    'opacity': (1 - scrollTop / headlineHeight)
  });
  $inner.children().css({
    'transform': 'translateY('+ scrollTop * 0.4 +'px)'
  });
  if (navOffset > headlineHeight) {
    $nav.addClass('scrolled');
  } else {
    $nav.removeClass('scrolled');
  }
});
!
999px

Console