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CSS Base

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Add External Stylesheets/Pens

Any URL's added here will be added as <link>s in order, and before the CSS in the editor. If you link to another Pen, it will include the CSS from that Pen. If the preprocessor matches, it will attempt to combine them before processing.

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You're using npm packages, so we've auto-selected Babel for you here, which we require to process imports and make it all work. If you need to use a different JavaScript preprocessor, remove the packages in the npm tab.

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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Use npm Packages

We can make npm packages available for you to use in your JavaScript. We use webpack to prepare them and make them available to import. We'll also process your JavaScript with Babel.

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Code Indentation


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Auto-Updating Preview

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

HTML Settings

Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

              <input id="search" placeholder="Search" />

<h1>Table of contents</h1>
  <li><a class="link-to-section" href="#section-1">Section One</a></li>
  <li><a class="link-to-section" href="#section-2">Section Two</a></li>
  <li><a class="link-to-section" href="#section-3">Section Three</a></li>
  <li><a class="link-to-section" href="#section-4">Section Four</a></li>

<h1 id="section-1" class="section-header">
  Section One
  <button class="back-to-top">Back to top</button>

<h1 id="section-2" class="section-header">
  Section Two
  <button class="back-to-top">Back to top</button>

<h1 id="section-3" class="section-header">
  Section Three
  <button class="back-to-top">Back to top</button>

<h1 id="section-4" class="section-header">
  Section Four
  <button class="back-to-top">Back to top</button>

              body, p, h1, h2 { margin: 0; }

body {
  font-family: -apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,"Helvetica Neue",Arial,sans-serif,"Apple Color Emoji","Segoe UI Emoji","Segoe UI Symbol";
  color: #333;
  font-size: 18px;
  background: white;
  padding-bottom: 2000px;

#search {
  display: block;
  width: 300px;
  padding: 10px;
  font-size: 20px;
  margin: 20px auto;

.back-to-top {
  padding-left: 10px;
  border: none;
  text-decoration: underline;
  background: none;

.section-header {
  margin-top: 600px;

/*  -------------------------  */
/*  --  The ease function  --  */
/*  -------------------------  */

function ease({
  startValue = 0,
  endValue = 1,
  durationMs = 200,
  onComplete = () => {},
}) {
  const raf = window.requestAnimationFrame || (func => window.setTimeout(func, 16));
  const stepCount = durationMs / 16;
  const valueIncrement = (endValue - startValue) / stepCount;
  const sinValueIncrement = Math.PI / stepCount;
  let currentValue = startValue;
  let currentSinValue = 0;
  function step() {
    currentSinValue += sinValueIncrement;
    currentValue += valueIncrement * (Math.sin(currentSinValue) ** 2) * 2;
    if (currentSinValue < Math.PI) {
    } else {


/*  ---------------------------  */
/*  --  Some usage examples  --  */
/*  ---------------------------  */

// This will scroll from the current position down to the element with a particular ID
document.querySelectorAll('.link-to-section').forEach(el => el.addEventListener('click', e => {
  // Side-note: NodeList.forEach() isn't supported everywhere
  const targetId ='href');
  const targetEl = document.querySelector(targetId);
  const targetPos = targetEl.getBoundingClientRect().top + window.scrollY;
    startValue: window.scrollY,
    endValue: targetPos,
    durationMs: 400,
    onStep: value => window.scroll(0, value),

// This will smoothly scroll from the current window position to the top.
// When at the top, it will focus the search box and remove the hash from the URL
document.querySelectorAll('.back-to-top').forEach(el => el.addEventListener('click', () => {
    startValue: window.scrollY,
    endValue: 0,
    onStep: value => window.scroll(0, value),
    onComplete: () => {
      // You wouldn't want to do these things before scrolling was finsihed,
      // they would snap the scroll immediately to the top of the page
      document.location.hash = '';

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