href="https://maxcdn.bootstrapcdn.com/font-awesome/4.6.3/css/font-awesome.min.css" code example

Example 1: fontawesome cdn

<link href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/5.13.0/css/all.min.css" rel="stylesheet">

Example 2: font awesome bootstrap cdn

<link rel="stylesheet" href="path/to/font-awesome/css/font-awesome.min.css">