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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

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.

!
Insecure Resource

The resource you are linking to is using the 'http' protocol, which may not work when the browser is using https.

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 

              
                <header id="header">
    <div class="logo">Smooth Scroll</div>
    <nav>
      <ul>
        <li><a href="#">Home</a></li>
        <li><a href="#">About</a></li>
        <li><a href="#">Offer</a></li>
        <li><a href="#">Contact</a></li>
      </ul>
    </nav>
  </header>

<div class="wrapper">

    <h1>Sagittis nisl rhoncus mattis rhoncus urna neque viverra justo nec</h1>
    <h3>Lorem ipsum dolor sit amet consectetur adipisicing elit. Ea necessitatibus assumenda cum perspiciatis quibusdam accusamus veniam dolores, pariatur maxime reiciendis laudantium eius facere ducimus, expedita harum quas? Expedita, doloribus officia!</h3>
    <p>Sagittis nisl rhoncus mattis rhoncus urna neque viverra justo necVehicula ipsum a arcu cursus vitae congue mauris. Enim neque volutpat ac tincidunt vitae semper quis lectus. Eleifend quam adipiscing vitae proin.</p>
    <hr />
    <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Commodo quis imperdiet massa tincidunt nunc pulvinar sapien. Odio euismod lacinia at quis risus sed vulputate odio. Posuere morbi leo urna molestie at. Montes nascetur ridiculus mus mauris vitae ultricies leo integer. Consectetur lorem donec massa sapien faucibus et molestie ac. Neque volutpat ac tincidunt vitae semper. Posuere lorem ipsum dolor sit amet consectetur. At lectus urna duis convallis convallis tellus id. Elementum nibh tellus molestie nunc non blandit massa enim nec. Auctor urna nunc id cursus metus aliquam eleifend. Diam quis enim lobortis scelerisque fermentum dui faucibus in. Sodales ut etiam sit amet nisl purus. Consequat semper viverra nam libero justo laoreet sit amet. Nunc faucibus a pellentesque sit amet porttitor. Egestas diam in arcu cursus euismod quis.</p>
    <p>Morbi tristique senectus et netus et malesuada fames ac turpis. Ornare massa eget egestas purus viverra accumsan. Elementum tempus egestas sed sed risus pretium quam vulputate dignissim. Lorem mollis aliquam ut porttitor leo. Duis convallis convallis tellus id interdum velit laoreet id. Vitae purus faucibus ornare suspendisse sed. Velit ut tortor pretium viverra suspendisse potenti nullam. Porttitor leo a diam sollicitudin tempor id eu nisl. Euismod in pellentesque massa placerat duis ultricies. Nec ullamcorper sit amet risus nullam. Est pellentesque elit ullamcorper dignissim cras tincidunt lobortis feugiat vivamus. Sagittis vitae et leo duis ut diam quam nulla porttitor. Vitae congue eu consequat ac felis donec. Tristique risus nec feugiat in fermentum posuere urna. Duis at consectetur lorem donec. Nulla pellentesque dignissim enim sit amet venenatis urna cursus. Lacinia quis vel eros donec ac odio. Sed arcu non odio euismod lacinia.</p>
    <p>Egestas sed tempus urna et pharetra. Volutpat est velit egestas dui id ornare arcu odio. Eget sit amet tellus cras adipiscing enim eu turpis egestas. Ut diam quam nulla porttitor. Nisi quis eleifend quam adipiscing vitae proin. Ullamcorper velit sed ullamcorper morbi tincidunt ornare massa eget egestas. Sed viverra tellus in hac habitasse. Pharetra et ultrices neque ornare aenean euismod elementum nisi quis. In fermentum et sollicitudin ac orci phasellus egestas tellus rutrum. Pharetra pharetra massa massa ultricies mi quis hendrerit. In hac habitasse platea dictumst quisque. Condimentum lacinia quis vel eros. Aliquet porttitor lacus luctus accumsan.</p>
    <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Commodo quis imperdiet massa tincidunt nunc pulvinar sapien. Odio euismod lacinia at quis risus sed vulputate odio. Posuere morbi leo urna molestie at. Montes nascetur ridiculus mus mauris vitae ultricies leo integer. Consectetur lorem donec massa sapien faucibus et molestie ac. Neque volutpat ac tincidunt vitae semper. Posuere lorem ipsum dolor sit amet consectetur. At lectus urna duis convallis convallis tellus id. Elementum nibh tellus molestie nunc non blandit massa enim nec. Auctor urna nunc id cursus metus aliquam eleifend. Diam quis enim lobortis scelerisque fermentum dui faucibus in. Sodales ut etiam sit amet nisl purus. Consequat semper viverra nam libero justo laoreet sit amet. Nunc faucibus a pellentesque sit amet porttitor. Egestas diam in arcu cursus euismod quis.</p>
    <p>Morbi tristique senectus et netus et malesuada fames ac turpis. Ornare massa eget egestas purus viverra accumsan. Elementum tempus egestas sed sed risus pretium quam vulputate dignissim. Lorem mollis aliquam ut porttitor leo. Duis convallis convallis tellus id interdum velit laoreet id. Vitae purus faucibus ornare suspendisse sed. Velit ut tortor pretium viverra suspendisse potenti nullam. Porttitor leo a diam sollicitudin tempor id eu nisl. Euismod in pellentesque massa placerat duis ultricies. Nec ullamcorper sit amet risus nullam. Est pellentesque elit ullamcorper dignissim cras tincidunt lobortis feugiat vivamus. Sagittis vitae et leo duis ut diam quam nulla porttitor. Vitae congue eu consequat ac felis donec. Tristique risus nec feugiat in fermentum posuere urna. Duis at consectetur lorem donec. Nulla pellentesque dignissim enim sit amet venenatis urna cursus. Lacinia quis vel eros donec ac odio. Sed arcu non odio euismod lacinia.</p>
    <p>Egestas sed tempus urna et pharetra. Volutpat est velit egestas dui id ornare arcu odio. Eget sit amet tellus cras adipiscing enim eu turpis egestas. Ut diam quam nulla porttitor. Nisi quis eleifend quam adipiscing vitae proin. Ullamcorper velit sed ullamcorper morbi tincidunt ornare massa eget egestas. Sed viverra tellus in hac habitasse. Pharetra et ultrices neque ornare aenean euismod elementum nisi quis. In fermentum et sollicitudin ac orci phasellus egestas tellus rutrum. Pharetra pharetra massa massa ultricies mi quis hendrerit. In hac habitasse platea dictumst quisque. Condimentum lacinia quis vel eros. Aliquet porttitor lacus luctus accumsan.</p>

</div>

<!-- Back to Top -->
<a href="#header" id="sf-back-to-top">&uarr;</a>
!

CSS 

              
                @import url('https://fonts.googleapis.com/css2?family=Inter:wght@100..900&display=swap');

html, body {
    margin: 0;
    padding: 0;
}

body {
    background-color: #f1f4f7;
    color: #3b495e;
    font-family: Inter;
    font-size: 1.2rem;
    line-height: 1.5;
}

.wrapper {
  width: 100%;
  max-width: 800px;
  margin: 50px auto;
  padding-left: 30px;
  padding-right: 30px;
  box-sizing: border-box;
}

header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    width: 100%;
    padding: 15px 20px;
    box-sizing: border-box;
    background-color: #212121;
    color: #fff;
}

header .logo {
  font-size: 30px;
  font-weight: bold;
}

header nav ul {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
}

header nav ul li {
  margin: 0 10px;
}

header nav ul li a {
  color: white;
  text-decoration: none;
}

header nav ul li a:hover {
  text-decoration: underline;
}

/* ---------------------------------------------------------- */
/*                    Snippflow Back to top                   */
/* ---------------------------------------------------------- */
html {
  scroll-behavior: smooth;
}

#sf-back-to-top {
    display: none;
    position: fixed;
    bottom: 20px;
    right: 20px;
    padding: 10px 15px;
    font-size: 16px;
    background-color: #46a787;
    color: #fff;
    text-decoration: none;
    border-radius: 3px;
    z-index: 100;
    transition: all 0.3s ease-in-out;
}

#sf-back-to-top:hover {
  transform: scale(1.1);
}
!

JS 

              
                $(document).ready(function() {

var backToTopButton = $('#sf-back-to-top');
  $(window).scroll(function() {
    if ($(window).scrollTop() > 100) {
      backToTopButton.fadeIn();
    } else {
      backToTopButton.fadeOut();
    }
  });

});
!
999px

Console