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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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Insecure Resource

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CSS

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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

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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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HTML 

              
                <div class="wrapper">
    <div>
      <p>Update 2016 - This has been fixed - YAY! :)</p>   
<p>UPDATE 2015-11-25 -- It looks like a fix for this is in the pipeline: <a href="https://codereview.chromium.org/1457783005">Chromium issue details</a>. Yay!</p>      
			<p>Try resizing this page, the border between two colours should be smooth in most browsers with the dotted line and colour interface matching up. In Chrome the position of the colour change is incorrect and jumps around</p>
      <p>According to <a href="https://code.google.com/p/chromium/issues/detail?id=233879">this bug</a> it is due to Chrome splitting the gradient into 256 sections, and so getting rounding down errors.</p>
      <p>Discovered via <a href="http://stackoverflow.com/questions/23627292/">this Stack Overflow question</a></p>
      <p>Update: Chrome 43 the jumping has been reduced ... but compare this page in Chrome and IE / Firefox to see the difference in rendering.</p>
	</div>
</div>

<div class="wrapper anim"><div>How it looks with gradient:</div></div>

<div class="wrapper anim correct"><div>What it should look like:</div></div>
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CSS 

              
                * { box-sizing: border-box; }

.wrapper {
  background: #f00;
  background: linear-gradient(to right, #ccc 66%, #2989d8 66%);
}

.wrapper div {
  margin: 0 0 6px;
  padding: 6px 12px;
  width:66%;
  border-right: 1px dotted white;
}

.correct {background: #2989d8}
.correct div {background: #ccc}

.anim {
animation: play 20s infinite;
}

@keyframes play {
   from { width: 500px; }
     to { width: 120%; }
}
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JS
!
999px

Console