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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

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About the <head>

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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).

Add External Stylesheets/Pens

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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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You can apply a script from anywhere on the web to your Pen. Just put a URL to it here and we'll add it, in the order you have them, before the JavaScript in the Pen itself.

If the script you link to has the file extension of a preprocessor, we'll attempt to process it before applying.

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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 

              
                <div id="carousel" class="snap">
  <div id="carousel-1">Item 1<br>Start scrolling ...</div>
  <div id="carousel-2">Item 2</div>
  <div id="carousel-3">Item 3</div>
</div>

<div id="controls">
  <button onclick="toggleSnap()">Turn Snapping <span id="otherSnappingState">off</span></button>
  <button onclick="toggleDirection()">Change scroll to <span id="otherScrollState">vertical</span></button>
</div>
!

CSS 

              
                #carousel {
  /* Ensure that the contents flow horizontally */
  overflow-x: auto;
  white-space: nowrap;
  display: flex;
}

#carousel.vertical {
  flex-direction: column;
}

/* 2018 spec - For Safari 11, Chrome 69+ */
#carousel.snap {
  scroll-snap-type: x mandatory;
  -webkit-overflow-scrolling: touch; /* Needed to work on iOS Safari */
}

#carousel.snap > div {
  scroll-snap-align: center;
}

#carousel.snap.vertical {
  flex-direction: column;
  scroll-snap-type: y mandatory;
}



/* 2015 spec - For Firefox, Edge, IE */
#carousel.snap {
  scroll-snap-type: mandatory;
  -ms-scroll-snap-type: mandatory;
  scroll-snap-points-x: repeat(100%);
  -ms-scroll-snap-points-x: repeat(100%);
}

#carousel.snap.vertical {
  scroll-snap-points-x: initial;
  -ms-scroll-snap-points-x: initial;
  scroll-snap-points-y: repeat(100%);
  -ms-scroll-snap-points-y: repeat(100%);
}


/* Below here is styling, not important for the actual example, just to make it look nice. No need to look down here! */

html, body {
  height: 100%;
  margin: 0;
  padding: 0;
}

#carousel {
  position: relative;
  width: 100%;
  height: 100%;
}

#carousel > div {
  min-width: 100%;
  min-height: 100%;
  display: flex;
  justify-content: center;
  align-items: center;
  text-align: center;
  color: #fff;
  font-size: 20px;
}

#carousel-1 {
  background-color: #e34747;
}

#carousel-2 {
  background-color: #5ab92c;
}

#carousel-3 {
  background-color: #226de2;
}

#controls {
  position: fixed;
  bottom: 10px;
  left: 10px;
}

#controls button {
  padding: 5px 10px;
}
!

JS 

              
                function toggleSnap() {
  var snapEnabled = document.getElementById('carousel').classList.toggle('snap');
  document.getElementById('otherSnappingState').innerText = snapEnabled ? 'off' : 'on';
}

function toggleDirection() {
  var isVertical = document.getElementById('carousel').classList.toggle('vertical');
  document.getElementById('otherScrollState').innerText = isVertical ? 'horizontal' : 'vertical';
}
!
999px

Console