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About the <head>
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About CSS Preprocessors
CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.
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.
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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If the script you link to has the file extension of a preprocessor, we'll attempt to process it before applying.
<iframe width="100%" height="300px" src="http://tuhoctin.net" name="iframe_a"></iframe>
<p><a href="http://tbit.vn" target="iframe_a">TBit - Diễn đàn công nghệ số</a></p>
<p>Khi nhấn vào liên kết trên sẽ hiển thị trang web được liên kết vào một iframe.</p>