In common.php

gistfile1.txt

        <link rel="stylesheet" type="text/css" href="css/winter.css" id="siteCSS"/>
        <script type="text/javascript">
 
        // Get current month
        var currDate=new Date();
        var currMonth = currDate.getDate();
 
        // Month returned by getDate() is 0 to 11 so add 1
        currMonth = parseInt(currMonth) + 1;
 
        // Based on month assign style sheet name
        var newCSS = "default.css";
        if (currMonth >= 1) newCSS = "winter.css"; // Month is January or greater
        if (currMonth >= 3) newCSS = 'spring.css'; // Month is March or greater
        if (currMonth >= 11) newCSS = 'winter.css'; // Month is June or greater
 
        // Assign new style sheet name as the new href for "siteCSS" LINK tag
        document.getElementById('siteCSS').href = newCSS;
 
    </script>
	</head>