/// Add the required stylesheets
$stylesheetshtml = '';
foreach ($CFG->stylesheets as $stylesheet) {
$stylesheetshtml .= '<link rel="stylesheet" type="text/css" href="'.$stylesheet.'" />'."\n";
}
$meta = $stylesheetshtml.$meta;
Actually, they get added to the $meta variable in print_header in lib/weblib.php