[PHP] Switch Styles.css code?

[PHP] Switch Styles.css code?

On my website, I am creating multiple styles.css. I am going to have a couple images at the top (little squares that are different colors). I need a PHP code that will switch the styles.css, keeping on the same URL, and being able to have different logos.

Just the straight-forward PHP code, no tutorials, is needed.

Thanks

<?php header("Content-type: text/css");
$white = '#fff';
$dkgray = '#333';
$dkgreen = '#008400';
?>
body {
background:<?=$white?>;
color:<?=$dkgray?>;
}
h1, h2, h3, h4 {
color:<?=$dkgreen?>;
}
blockquote {
color:<?=$dkgreen?>;
}