Row in Flexbox wrap, but align-content: space-between doesn't work
<p>I have some problems with the property "align-content: space-between".
With "justify-content" i add "space-between" the flex-items and now i want to add space between the different wrapped rows.</p>

<p>CSS</p>

<pre><code>article &gt; div {
    align-content: space-between;
    display: flex;
    flex-wrap: wrap;
    justify-content: space-between;
}
#preview {
    background-color: black;
    width: 49.5%;
    text-align: center;
}
</code></pre>

<p>HTML</p>

<pre><code>&lt;article&gt;
  &lt;div&gt;
&lt;?php if (have_posts()) : while (have_posts()) : the_post(); ?&gt;

     &lt;div id="preview"&gt; 

        &lt;?php if (has_post_thumbnail()) { ?&gt;
        &lt;a href="&lt;?php the_permalink() ?&gt;"&gt;&lt;?php the_post_thumbnail(); ?&gt;&lt;/a&gt;
        &lt;?php } ?&gt; 

        &lt;h2&gt;&lt;a href="&lt;?php the_permalink() ?&gt;"&gt;&lt;?php the_title(); ?&gt;&lt;/a&gt;&lt;/h2&gt;


     &lt;/div&gt;


&lt;?php endwhile; ?&gt;
  &lt;/div&gt;
&lt;?php endif; ?&gt;

&lt;/article&gt;
</code></pre>