将CSS3应用于PHP DOMDocument

我正在尝试将CSS应用于通过PHP创建的DOMDocument。然而，即使我使用jQuery来应用样式，它也不起作用。我举了一个例子：

<div id="content">
<p class="intro">Below are some of the YouTube videos I've made.
    <br />Feel free to take a look!</p>
<div id="video-content">
    <?php include '../resources/php/functions.php';
            $functions=new Functions;
            $functions->getVideos();
    ?>
    <script type="text/javascript">
        $(window).load(function() {
            $('iframe-video').css({
                "margin-left": "auto"
            });
            $('iframe-video').css({
                "margin-right": "auto"
            });
            $('iframe-video').css({
                "margin-bottom": "35px"
            });
        });
    </script>
</div>

$functions->getVideos();成功返回视频，并显示视频。他们还上了iframe视频课。然而，上面的CSS实际上并不适用于它

如何更改PHP DOMDocument生成的元素的CSS？

PHP代码如下：

public function getVideos() {
        $doc = new DOMDocument;
        libxml_use_internal_errors(true);
        $doc->loadHTMLFile('http://www.youtube.com/user/HathorArts/videos');
        libxml_use_internal_errors(false);
        $xpath = new DOMXPath($doc);
        $nodes = $xpath -> query('//a[@class="ux-thumb-wrap yt-uix-sessionlink yt-uix-contextlink yt-fluid-thumb-link contains-addto "]');
        // Get the URLS for the videos, and build the iFrames for them.
        $output = new DOMDocument;
        foreach($nodes as $i => $node) {
            // Creates the video URL for the iFrame
            $temp_url = $node->getAttribute('href');
            $replace_url = str_replace("/watch?v=", "", $temp_url);
            $video_url = ("//www.youtube.com/embed/" . $replace_url . "?rel=0");
            // Builds the iFrme
            $iframe = $output->createElement('iframe');
            $iframe->setAttribute('class', 'iframe-video');
            $iframe->setAttribute('width', '560');
            $iframe->setAttribute('height', '315');
            $iframe->setAttribute('src', $video_url);
            $iframe->setAttribute('frameborder', "0");
            // Outputs the iFrame
            $output->appendChild($iframe);
        }
        // Sends the output to the index file
        echo $output -> saveHTML();
    }