Pen Settings



CSS Base

Vendor Prefixing

Add External Stylesheets/Pens

Any URLs added here will be added as <link>s in order, and before the CSS in the editor. You can use the CSS from another Pen by using its URL and the proper URL extension.

+ add another resource


Babel includes JSX processing.

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.

+ add another resource


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.


Auto Save

If active, Pens will autosave every 30 seconds after being saved once.

Auto-Updating Preview

If enabled, the preview panel updates automatically as you code. If disabled, use the "Run" button to update.

Format on Save

If enabled, your code will be formatted when you actively save your Pen. Note: your code becomes un-folded during formatting.

Editor Settings

Code Indentation

Want to change your Syntax Highlighting theme, Fonts and more?

Visit your global Editor Settings.



    <li><a href="#section-1">Section 1</a></li>
    <li><a href="#section-2">Section 2</a></li>
    <li><a href="#section-3">Section 3</a></li>
    <li><a href="#section-4">Section 4</a></li>
    <li><a href="#section-5">Section 5</a></li>
    <li><a href="#section-6">Section 6</a></li>
    <li><a href="#section-7">Section 7</a></li>
    <li><a href="#section-8">Section 8</a></li>
    <li><a href="#section-9">Section 9</a></li>

  <section id="section-1">
    <h1>Section 1</h1>
    <p>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Officiis, blanditiis expedita? Earum eligendi pariatur quaerat quos expedita ab quibusdam ratione veniam in, mollitia fuga repudiandae?</p>
  <section id="section-2">
    <h1>Section 2</h1>
    <p>Ratione nulla nam, ipsa dignissimos corrupti veniam nostrum, laudantium asperiores sequi numquam placeat velit voluptate in praesentium non labore unde incidunt laborum maxime quae magni.</p>
  <section id="section-3">
    <h1>Section 3</h1>
    <p>Soluta quibusdam ad nostrum vel voluptate delectus sequi dolores quia quaerat officia corrupti, aperiam fugit facere debitis repudiandae praesentium sapiente inventore repellendus, nemo commodi alias!</p>
  <section id="section-4">
    <h1>Section 4</h1>
    <p>Aliquid aliquam magnam ducimus similique obcaecati, unde exercitationem laborum incidunt, quas in ipsum inventore nostrum? Blanditiis optio cumque earum iste odio! Alias sint accusamus repudiandae.</p>
  <section id="section-5">
    <h1>Section 5</h1>
    <p>Officia ipsum fugit iure eaque quisquam error tempore earum enim illum, delectus officiis incidunt corrupti aliquid nam quas perspiciatis eveniet doloremque quod labore? Doloremque, ipsum?</p>
  <section id="section-6">
    <h1>Section 6</h1>
    <p>Aperiam repellat dignissimos fugiat possimus esse, suscipit neque nisi libero alias obcaecati ipsam, porro illo corrupti nostrum reprehenderit unde, illum in laudantium impedit. Modi, veniam.</p>
  <section id="section-7">
    <h1>Section 7</h1>
    <p>Cum asperiores temporibus itaque consequatur quod inventore, quia quis explicabo dicta esse minus voluptatem reiciendis eveniet animi, necessitatibus illum dolorem doloremque repellat placeat, dolores eaque.</p>
  <section id="section-8">
    <h1>Section 8</h1>
    <p>Optio qui, omnis itaque rerum iusto molestiae necessitatibus deleniti quod tenetur id perspiciatis voluptatum dolorum quisquam eius ipsum non architecto labore! Distinctio, tenetur. Officiis, necessitatibus?</p>
  <section id="section-9">
    <h1>Section 9</h1>
    <p>Rem iste iure blanditiis excepturi esse nisi corrupti sequi, illo, laborum quo quis quaerat assumenda perspiciatis quod fuga vel laudantium doloribus architecto tempora omnis earum!</p>

  &copy;2018 Footer


                html {
  scroll-behavior: smooth;
body {
  margin: 0;
  display: grid;
  grid-template-columns: min-content 1fr;
  font-family: system-ui, sans-serif;
  /* this breaks position sticky in Firefox */
  /* overflow-x: hidden; */
header {
  grid-column: 1 / 3;
  background: #455A64;
  color: white;
  padding: 4rem;
  text-align: center;
nav {
  white-space: nowrap;
  background: #37474F;
nav ul {
  list-style: none;
  margin: 0;
  padding: 0;
/* Only stick if you can fit */
@media (min-height: 300px) {
  nav ul {
    position: sticky;
    top: 0;
nav ul li a {
  display: block;
  padding: 0.5rem 1rem;
  color: white;
  text-decoration: none;
nav ul li a.current {
  background: black;
main {
  padding-bottom: 40rem;
section {
  padding: 2rem;
  margin: 0 0 2rem 0;
footer {
  grid-column: 1 / 3;
  background: #607D8B;
  padding: 5rem 1rem;


                let mainNavLinks = document.querySelectorAll("nav ul li a");
let mainSections = document.querySelectorAll("main section");

let lastId;
let cur = [];

// This should probably be throttled.
// Especially because it triggers during smooth scrolling.
// You could do like...
// window.addEventListener("scroll", () => {
//    _.throttle(doThatStuff, 100);
// });
// Only not doing it here to keep this Pen dependency-free.

window.addEventListener("scroll", event => {
  let fromTop = window.scrollY;

  mainNavLinks.forEach(link => {
    let section = document.querySelector(link.hash);

    if (
      section.offsetTop <= fromTop &&
      section.offsetTop + section.offsetHeight > fromTop
    ) {
    } else {