Include: CSS with .php file extension?

gnarf nailed it.

I do:

<link rel="stylesheet" type="text/css" media="screen" href="<? echo TMPL ?>css/name-of-file.css.php">

and then in top of your .css.php file:

<?
header('Content-Type: text/css');
// print out your php-driven css...
?>

If you have a file called css.php just make sure the first lines set the proper content-type header. You may also want to split your session setup stuff (if there is any) into a bootstrap.php if you haven't already. A quick example of loading some style info from a databse:

<?php 
  header("Content-Type: text/css"); 
  include('bootstrap.php');
  // fetch some information to print out our styles
  $result = mysql_query("SELECT * FROM site_styles");
  while ($row = mysql_fetch_assoc($result)) {
    echo $row["selector"]." {\n".$row["css"]."\n}\n";
  }
?>

From your other php file, just output the tag to include the css.php, you do not want to use the php include() function for this task!

<link rel="stylesheet" type="text/css" href="css.php"/>

Although since most browsers will cache your css file pretty aggressively, you might find that dynamically changing the contents of that file doesn't do much good. You could force that to update by adding a get parameter to the href of the link like so:

<link rel="stylesheet" type="text/css" href="css.php?<?php echo $cssversion ?>"/>

Although this is going to completely reload your css file every time that parameter changes. It is generally better practice to serve up static css files for this reason. If you have some styles that need to be loaded from configuration parameters, etc, that don't change very often, the first example should work for you quite well.