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addRule('body', 'background-color', '#f0f0f0'); // output the CSS header('Content-Type: text/css'); echo $css->parse(); ?>Package library: In example 2, the code requires the use of a PHP library to generate CSS. It's unclear which library is being used since the code only includes the generic statement `require_once('vendor/autoload.php')`. Some popular PHP libraries for generating CSS include PHPCSS and Expose.