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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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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-.

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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 

              
                <main class="Loop js-loop">
  <section class="one">
    <h1>One</h1>
  </section>
  <section class="two">
    <h1>For</h1>
  </section>
  <section class="three">
    <h1>All</h1>
  </section>
  <section class="four">
    <h1>And</h1>
  </section>
  <section class="three">
    <h1>All</h1>
  </section>
  <section class="two">
    <h1>For</h1>
  </section>

  <!--
  These blocks are the same as the first blocks to get that looping illusion going.
  You need to add clones to fill out a full viewport height.
  -->
  <section class="one is-clone">
    <h1>One</h1>
  </section>
  <section class="two is-clone">
    <h1>For</h1>
  </section>
</main>
!

CSS 

              
                html,
body {
  height: 100%;
  overflow: hidden;
}

.Loop {
  position: relative;
  height: 100%;
  overflow: auto;
  -webkit-overflow-scrolling: touch;
}

section {
  position: relative;
  text-align: center;
  min-height: 300px;
  max-height: 700px;
  height: 80%;
}

::scrollbar {
  display: none;
}







body {
  font-family: "Avenir Next", Helvetica, sans-serif;
  font-weight: normal;
  font-size: 100%;
}

.one {
  background: #81234e;
}

.two {
  background: #df5252;
}

.three {
  background: #ff9a56;
}

.four {
  background: #371465;
}

h1 {
  margin: 0;
  position: absolute;
  top: 50%;
  transform: translateY(-50%);
  width: 100%;
  font-size: 80px;
  letter-spacing: 5px;
  color: #fff;
  text-transform: uppercase;
}
!

JS 

              
                var doc = window.document,
  context = doc.querySelector('.js-loop'),
  clones = context.querySelectorAll('.is-clone'),
  disableScroll = false,
  scrollHeight = 0,
  scrollPos = 0,
  clonesHeight = 0,
  i = 0;

function getScrollPos () {
  return (context.pageYOffset || context.scrollTop) - (context.clientTop || 0);
}

function setScrollPos (pos) {
  context.scrollTop = pos;
}

function getClonesHeight () {
  clonesHeight = 0;

  for (i = 0; i < clones.length; i += 1) {
    clonesHeight = clonesHeight + clones[i].offsetHeight;
  }

  return clonesHeight;
}

function reCalc () {
  scrollPos = getScrollPos();
  scrollHeight = context.scrollHeight;
  clonesHeight = getClonesHeight();

  if (scrollPos <= 0) {
    setScrollPos(1); // Scroll 1 pixel to allow upwards scrolling
  }
}

function scrollUpdate () {
  if (!disableScroll) {
    scrollPos = getScrollPos();

    if (clonesHeight + scrollPos >= scrollHeight) {
      // Scroll to the top when you’ve reached the bottom
      setScrollPos(1); // Scroll down 1 pixel to allow upwards scrolling
      disableScroll = true;
    } else if (scrollPos <= 0) {
      // Scroll to the bottom when you reach the top
      setScrollPos(scrollHeight - clonesHeight);
      disableScroll = true;
    }
  }

  if (disableScroll) {
    // Disable scroll-jumping for a short time to avoid flickering
    window.setTimeout(function () {
      disableScroll = false;
    }, 40);
  }
}

function init () {
  reCalc();
  
  context.addEventListener('scroll', function () {
    window.requestAnimationFrame(scrollUpdate);
  }, false);

  window.addEventListener('resize', function () {
    window.requestAnimationFrame(reCalc);
  }, false);
}

if (document.readyState !== 'loading') {
  init()
} else {
  doc.addEventListener('DOMContentLoaded', init, false)
}








// Just for this demo: Center the middle block on page load
window.onload = function () {
  setScrollPos(Math.round(clones[0].getBoundingClientRect().top + getScrollPos() - (context.offsetHeight - clones[0].offsetHeight) / 2));
};
!
999px

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