title: How to position an <input> in the center of the <div>
body: <p>My HTML looks like this:</p>
  
  <pre><code>&lt;div class="item"&gt;
      &lt;div class="check"&gt;
        &lt;input type="checkbox"&gt;
      &lt;/div&gt;
      &lt;div class="descr"&gt; ... &lt;/div&gt;
      &lt;div class="details"&gt; ... &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>How do I align the checkbox in the middle of the <code>div.check</code>, both horizontally and vertically? (the height of the <code>".item"</code> div is dynamic)</p>