Since cakephp 1.3, build-in css compression has stopped working. at least for me. however, it's very easy to get it working again.
grab csspp from here and put it in your vendor directory so it looks something like this (app/vendors/csspp/csspp.php)
in your core.php file in app/config, uncomment Configure::write('Asset.filter.css', 'css.php');
in your css.php under app/webroot, modify make_clean_css function so that it looks something like this
function make_clean_css($path, $name)
App::import('Vendor', 'csspp' . DS . 'csspp');
$data = file_get_contents($path);
$csspp = new csspp($name,'');
$output = $csspp->process();
$ratio = 100 - (round(strlen($output) / strlen($data), 3) * 100);
$output = " /* file: $name, ratio: $ratio% */ " . $output;
and that should be it. if it doesnt work for some reason,
change line 82 in your app/webroot/css.php to
if (file_exists($cachepath) && 0)
so you won't be looking at cached file when u debug.