PHP-CSS-ParserのDeclarationBlockは__toString()が使える ref: http://qiita.com/items/2837

file0.txt

<?php
require(dirname(__FILE__) . '/../CSSParser.php');
$cssFile = 'epub/OEBPS/stylesheet.css';

$parser = new CSSParser(file_get_contents($cssFile));
$css = $parser->parse();

foreach ($css->getAllDeclarationBlocks() as $db) {
    echo $db, PHP_EOL;
    echo '---------------------------------------------', PHP_EOL;
}