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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).

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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

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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 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>
!

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;
}
!

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();
!
999px

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