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EXTERNAL stylesheet use - Using HTML with CSS - HTML
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HTML - Using HTML with CSS - External stylesheet use
External Stylesheet Use

Use the link attribute in the document's head:

<head>
    <link rel="stylesheet" type="text/css" href="stylesheet.css">
</head>

You can also use stylesheets provided from websites via a content delivery network, or CDN for short. (for example, Bootstrap):

<head>
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" integrity="sha384-BVYiiSIFeK1dGmJRAkycuHAHRg32OmUcww7on3RYdg4Va+PmSTsz/K68vbdEjh4u" crossorigin="anonymous">
</head>

Generally, you can find CDN support for a framework on its website.

 
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https://develop.horje.com/learn/1434/reference

 

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