PHP Simple HTML DOM Parser - find function not working with multiple classes

I am trying to parse a certain section out of a website. I know my cURL statement is working and grabbing the raw HTML, because I can echo the results of the cURL command and see the web page contents on my server.

Here is what I am trying to parse out:

enter image description here

As you can see I am trying to parse out the "mw-scrollable-news.collection.j-tabPane.is-active.j-scrollViewport".

My code looks like this, I am using the exact CSS selector as is given on the site:

$html = str_get_html($results); // $results is the results of the cURL
$articleDivArray = $html->find('mw-scrollable-news.collection.j-tabPane.is-active.j-scrollViewport');

However when I do a:

print_r($articleDivArray);

It brings back an empty:

array(0) {
}

Here is what the raw HTML looks like:

<div class="collection__list j-scrollElement" data-type="Other" data-showTimestamp="True" data-showImage="False" data-showProvider="True" data-showByline="False" >
<div data-docid="1341791639" class="element element--article no-image j-scrollByElement">

    <div class="article__content">

            <h3 class="article__headline"><a class="link" rel="nofollow" target="_blank" data-source="seekingalpha.com" href="https://seekingalpha.com/news/3392514-new-age-beverages-enters-market-offering-agreement?source=marketwatch">New Age Beverages enters into At the Market Offering Agreement</a></h3>
        <p class="article__summary">New Age Beverages enters into At the Market Offering Agreement</p>


        <ul class="article__details">
            <li data-est="2018-09-24T13:51:00" class="article__timestamp">Sep. 24, 2018 at 1:51 p.m. ET</li>

            <li class="article__provider">on Seeking Alpha</li>

        </ul>
    </div>

</div>
<div data-docid="1341775218" class="element element--article no-image j-scrollByElement">

    <div class="article__content">

            <h3 class="article__headline"><a class="link" rel="nofollow" target="_blank" data-source="fool.com" href="https://www.fool.com/investing/2018/09/24/big-highs-wont-last-for-new-age-beverage-stock.aspx?source=djc&utm_campaign=article&utm_medium=feed&utm_source=djc">Big Highs Won&#x27;t Last for New Age Beverage Stock</a></h3>
        <p class="article__summary"></p>


        <ul class="article__details">
            <li data-est="2018-09-24T09:00:00" class="article__timestamp">Sep. 24, 2018 at 9:00 a.m. ET</li>

            <li class="article__provider">on Motley Fool</li>

        </ul>
    </div>

and so on etc...

Am I doing something wrong?