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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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CSS

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CSS Base

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JavaScript

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JavaScript preprocessors can help make authoring JavaScript easier and more convenient.

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Babel includes JSX processing.

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HTML 

              
                <main>
  <div class="wrapper">
    <article class="flow">
      <h1>Inheritance cascades downwards</h1>
      <p>Properties that can be inherited cascade downwards, and child elements will get a computed value which represents its parent’s value. This means that if a parent has <code>font-weight</code> set to <code>300</code>: all child elements will be light unless they have <code>font-weight</code> set to a different value or the user agent stylesheet has a value for <code>font-weight</code>, for that element. </p>
      <p>That is the case here. All text is <code>font-weight: 300</code>, but <code>&lt;span&gt;</code> elements have a <code>font-weight</code> of <code>700</code> which overrides the inheritance. <span>This sentence is wrapped in a <code>&lt;span&gt;</code>, so the text is bold weight</span>.</p>
      <p>Notice also how the inline code <em>also</em> inherits the bold <code>font-weight</code>.</p>
    </article>
  </div>
</main>
!

CSS 

              
                article {
  font-weight: 300;
}

span {
  font-weight: 700;
}
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JS
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999px

Console