PHP を使用して CSS ファイルから「postclass」を含むクラス名を抽出するにはどうすればよいですか?

function parse($file) {
    $css = file_get_contents($file);
    preg_match_all('/(?ims)([a-z0-9\s\.\:#_\-@,]+)\{([^\}]*)\}/', $css, $arr);
    $result = array();
    foreach ($arr[0] as $i => $x) {
        $selector = trim($arr[1][$i]);
        $rules = explode(';', trim($arr[2][$i]));
        $rules_arr = array();
        foreach ($rules as $strRule) {
            if (!empty($strRule)) {
                $rule = explode(':', $strRule);
                $rules_arr[trim($rule[0])] = trim($rule[1]);
            }
        }
        $selectors = explode(',', trim($selector));
        foreach ($selectors as $strSel) {
            $result[$strSel] = $rules_arr;
        }
    }
    return $result;
}

$css = parse('css/'.$user['blog'].'.php');
echo $css['#selector']['color']; // Outputs the value of the 'color' property for the '#selector' class with 'postclass' in its name