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HTML

About HTML Preprocessors

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

In CodePen, whatever you write in the HTML editor is what goes within the <body> tags in a basic HTML5 template. So you don't have access to higher-up elements like the <html> tag. If you want to add classes there that can affect the whole document, this is the place to do it.

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-.

We offer two popular choices: Autoprefixer (which processes your CSS server-side) and -prefix-free (which applies prefixes via a script, client-side).

Add External Stylesheets/Pens

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You can apply CSS to your Pen from any stylesheet on the web. Just put a URL to it here and we'll apply it, in the order you have them, before the CSS in the Pen itself.

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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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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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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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About Packages

Using packages here is powered by Skypack, which makes packages from npm not only available on a CDN, but prepares them for native JavaScript ES6 import usage.

All packages are different, so refer to their docs for how they work.

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HTML 

              
                <p>不设置flex-basis，占据宽度为项目宽度</p>
<div class="wrap">
	<div class="item">宽度200</div>
	<div class="item">宽度200</div>
	<div class="item">宽度200</div>
</div>
<p>设置flex-basis，占据宽度为flex-basis</p>
<div class="wrap">
	<div class="item setFlexBasis">宽度100</div>
	<div class="item setFlexBasis">宽度100</div>
	<div class="item setFlexBasis">宽度100</div>
</div>
<p>设置flex-basis，受限于min-width和max-width</p>
<div class="wrap">
	<div class="item setFlexBasis minWidth">宽度300</div>
	<div class="item setFlexBasis maxWidth">宽度50</div>
	<div class="item setFlexBasis">宽度100</div>
</div>
<p>设置flex-basis为0时，会尽可能压缩</p>
<div class="wrap">
	<div class="item setFlexBasis0">宽度</div>
	<div class="item setFlexBasis0">宽度</div>
	<div class="item setFlexBasis0">宽度</div>
</div>
<p>设置flex-basis为auto时，且不设置宽度时，占用空间由内容决定</p>
<div class="wrap">
	<div class="item setFlexBasisAuto">宽度</div>
	<div class="item setFlexBasisAuto">宽度</div>
	<div class="item setFlexBasisAuto">宽度</div>
</div>
!

CSS 

              
                .wrap
	display flex
	border 4px solid #000
	width 800px
	.item
		width 200px
		height 200px
		&:nth-child(1)
			background #eee
		&:nth-child(2)
			background red
		&:nth-child(3)
			background yellow
		&.setFlexBasis
			flex-basis 100px
			&.minWidth
				min-width 300px
			&.maxWidth
				max-width 50px
		&.setFlexBasis0
			flex-basis 0
		&.setFlexBasisAuto
			flex-basis auto
			width auto
!

JS
!
999px

Console