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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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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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About JavaScript Preprocessors

JavaScript preprocessors can help make authoring JavaScript easier and more convenient. For instance, CoffeeScript can help prevent easy-to-make mistakes and offer a cleaner syntax and Babel can bring ECMAScript 6 features to browsers that only support ECMAScript 5.

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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.

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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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About External Resources

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.

You can also link to another Pen here, and we'll pull the JavaScript from that Pen and include it. If it's using a matching preprocessor, we'll combine the code before preprocessing, so you can use the linked Pen as a true dependency.

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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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HTML

            
              <div class="container">
  <div class="backdrop">
    <div class="highlights"></div>
  </div>
  <textarea>This demo shows how to highlight bits of text within a textarea. Alright, that's a lie. You can't actually render markup inside a textarea. However, you can fake it by carefully positioning a div behind the textarea and adding your highlight markup there. JavaScript takes care of syncing the content and scroll position from the textarea to the div, so everything lines up nicely. Hit the toggle button to peek behind the curtain. And feel free to edit this text. All capitalized words will be highlighted.</textarea>
</div>
<button>Toggle Perspective</button>
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CSS

            
              @import url(https://fonts.googleapis.com/css?family=Open+Sans);

*, *::before, *::after {
  box-sizing: border-box;
}

body {
  margin: 30px;
  background-color: #f0f0f0;
}

.container, .backdrop, textarea {
  width: 460px;
  height: 180px;
}

.highlights, textarea {
  padding: 10px;
  font: 20px/28px 'Open Sans', sans-serif;
  letter-spacing: 1px;
}

.container {
  display: block;
  margin: 0 auto;
  transform: translateZ(0);
  -webkit-text-size-adjust: none;
}

.backdrop {
  position: absolute;
  z-index: 1;
  border: 2px solid #685972;
  background-color: #fff;
  overflow: auto;
  pointer-events: none;
  transition: transform 1s;
}

.highlights {
	white-space: pre-wrap;
	word-wrap: break-word;
	color: transparent;
}

textarea {
  display: block;
  position: absolute;
  z-index: 2;
  margin: 0;
  border: 2px solid #74637f;
  border-radius: 0;
  color: #444;
  background-color: transparent;
  overflow: auto;
  resize: none;
  transition: transform 1s;
}

mark {
  border-radius: 3px;
  color: transparent;
  background-color: #b1d5e5;
}

button {
  display: block;
  width: 300px;
  margin: 30px auto 0;
  padding: 10px;
  border: none;
  border-radius: 6px;
  color: #fff;
  background-color: #74637f;
  font: 18px 'Opens Sans', sans-serif;
  letter-spacing: 1px;
  appearance: none;
  cursor: pointer;
}

.perspective .backdrop {
  transform:
    perspective(1500px)
    translateX(-125px)
    rotateY(45deg)
    scale(.9);
}

.perspective textarea {
  transform:
    perspective(1500px)
    translateX(155px)
    rotateY(45deg)
    scale(1.1);
}

textarea:focus, button:focus {
  outline: none;
  box-shadow: 0 0 0 2px #c6aada;
}
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JS

            
              var $container = $('.container');
var $backdrop = $('.backdrop');
var $highlights = $('.highlights');
var $textarea = $('textarea');
var $toggle = $('button');

// yeah, browser sniffing sucks, but there are browser-specific quirks to handle that are not a matter of feature detection
var ua = window.navigator.userAgent.toLowerCase();
var isIE = !!ua.match(/msie|trident\/7|edge/);
var isWinPhone = ua.indexOf('windows phone') !== -1;
var isIOS = !isWinPhone && !!ua.match(/ipad|iphone|ipod/);

function applyHighlights(text) {
  text = text
    .replace(/\n$/g, '\n\n')
    .replace(/[A-Z].*?\b/g, '<mark>$&</mark>');
  
  if (isIE) {
    // IE wraps whitespace differently in a div vs textarea, this fixes it
    text = text.replace(/ /g, ' <wbr>');
  }
  
  return text;
}

function handleInput() {
  var text = $textarea.val();
  var highlightedText = applyHighlights(text);
  $highlights.html(highlightedText);
}

function handleScroll() {
  var scrollTop = $textarea.scrollTop();
  $backdrop.scrollTop(scrollTop);
  
  var scrollLeft = $textarea.scrollLeft();
  $backdrop.scrollLeft(scrollLeft);  
}

function fixIOS() {
  // iOS adds 3px of (unremovable) padding to the left and right of a textarea, so adjust highlights div to match
  $highlights.css({
    'padding-left': '+=3px',
    'padding-right': '+=3px'
  });
}

function bindEvents() {
  $textarea.on({
    'input': handleInput,
    'scroll': handleScroll
  });

  $toggle.on('click', function() {
    $container.toggleClass('perspective');
  });  
}

if (isIOS) {
  fixIOS();
}

bindEvents();
handleInput();
!
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