PHP CSS Stylesheet with variables and cache headers

style.php

<?php

/**
 * Adding Cache Headers and ETag to example: http://sperling.com/examples/pcss/
 */
 
class PHPStyle 
{

    public static function setHeaders($filename="style.css",$type="text/css")
    {
        $mod = date ("Y-m-d::H:i:s.", getlastmod()); 
        $etag = $filename.$mod;
        $headers = apache_request_headers();  
        $isCached = isset($headers['If-None-Match']) && $headers['If-None-Match']==$etag;
        
        header("Content-type: $type");
        if ($isCached) {
            header('HTTP/1.1 304 Not Modified');
            header("Cache-Control: max-age=604800");
            header("Pragma: cache");
            header("ETag: $etag");
            die();
        } else {
            header("Etag: $etag");
            header("Pragma: cache");
            header("Cache-Control: max-age=604800");
            header("Content-Disposition: inline; filename=\"$filename\"");
        }
    }
    
}

$test = PHPStyle::setHeaders();

$blue = "blue";
$green = "green";

$sheet = <<<CSS

/* --- start of css --- */
h1 {
    color: $blue; 
    font-weight: bold;
    font-size: 1.2em;
    text-align: left;
    }
h2 {
    color:$green;
}
/* --- end of css --- */
CSS;

echo $sheet;