Html: index.html
<html>
<head>
<title>Join Files Header</title>
<!-- HERE -->
<link href="css/main.css" join="css/css1.css, css/css2.css" media="all" rel="stylesheet" type="text/css" />
</head>
<body>
<span class="class1 class2">Joined</span>
</body>
</html>CSS: css/css1.css
span.class1 {
color: red;
}CSS: css/css2.css
span.class2 {
font-size: 20px;
}