title: sortable - items changes top margin while dragging
body: <p>Why top and/or bottom margin of <code>child</code> is changed while dragging them?<br>
  I need them to stay inline.</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>$('.parent').sortable({
   containment: "parent",
   axis: "x",
  });</code></pre>
  <pre class="snippet-code-css lang-css prettyprint-override"><code>.parent{
  text-align:center;
  }
  
  .child{
  display:inline-block;
  padding:2px 9px;
  border-radius:9px;
  background:gold;
  margin:0 9px;
  cursor:pointer;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;link rel="stylesheet" href="https://ajax.googleapis.com/ajax/libs/jqueryui/1.12.1/themes/smoothness/jquery-ui.css"&gt;
  &lt;script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"&gt;&lt;/script&gt;
  &lt;script src="https://ajax.googleapis.com/ajax/libs/jqueryui/1.12.1/jquery-ui.min.js"&gt;&lt;/script&gt;
  &lt;div class='parent'&gt;
  &lt;div class='child'&gt;323&lt;/div&gt;
  &lt;div class='child'&gt;525&lt;/div&gt;
  &lt;div class='child'&gt;727&lt;/div&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>