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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>

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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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-.

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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="wrap">
  <h1>run-in box</h1>
  <p>run-in框的行为如下：</p>
  <ol>
    <li>如果run-in框包含一个块框，那么run-in框变为块框。</li>
    <li>如果run-in框的后继兄弟元素为块框（非浮动，非绝对定位），那么run-in框变为该块框的第一个行内框。run-in不能插入本身为run-in的块中，也不能插入块中已有run-in的块中。</li>
    <li>否则，run-in框变为块框。</li>
  </ol>
  <p>浏览器支持：IE8+，chrome（unsupport）</p>
  <h2>case 1</h2>
  <div class="run-in-box">
    <p>some text...</p>
  </div>
  <div>some other text....</div>
  <h2>case 2</h2>
  <h3 class="run-in-box">A run-in heading.</h3>
  <p>And a paragraph of text that follows it.</p>
  <h2>case 3</h2>
  <h3 class="run-in-box">A run-in heading.</h3>
  <span>And a span of text that follows it.</span>
</div>
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CSS 

              
                .wrap {
  width: 800px;
  margin: 0 auto;
}

.run-in-box {
  display: run-in;
}

li {
  line-height: 1.6;
}

h2 {
  margin-top: 60px;
}
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JS
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999px

Console