CSS media queries dynamically introduce resource files
1. Grammar specification
<link rel="stylesheet" media="mediatype and|not|only (media feature)" href="mystylesheet.css">
2. Examples
<link rel="stylesheet" href="style320.css" media="screen and (min-width:320px)">
<link rel="stylesheet" href="style640.css" media="screen and (min-width:640px)">