title: How can I put elements underneath each other in flex display?
body: <p>Here is my code:</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-css lang-css prettyprint-override"><code>.menu_box {
    background-color: whitesmoke;
    margin: auto;
    position: fixed;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;
    border-radius: 3px;
    width: 100vh;
    height: 60vh;
    display: flex;
    flex-direction: column;
  }
  
  .menu_box_body {
    flex-grow: 1;
    display: flex;
    flex-direction: row;
    flex-wrap: wrap;
    width:100%;
  }
  
  .menu_box_header {
    height: 45px;
    background-color: #f1f1f1;
    border-bottom: 1px solid #e1e1e1;
    position: relative;
    margin-bottom: 10px;
    width: 100%;
  }
  
  .menu_options {
    border: 1px solid #e1e1e1;
    display:flex;
    align-items:center;
    justify-content:center;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet" /&gt;
  &lt;div class="menu_box"&gt;
    &lt;div class="menu_box_header"&gt;
    &lt;/div&gt;
    &lt;div class="menu_box_body"&gt;
      &lt;div class="menu_options col-xs-6"&gt;&lt;div&gt;{icon}&lt;/div&gt;&lt;h3&gt;part1&lt;/h3&gt;&lt;/div&gt;
      &lt;div class="menu_options col-xs-6"&gt;&lt;div&gt;{icon}&lt;/div&gt;&lt;h3&gt;part2&lt;/h3&gt;&lt;/div&gt;
      &lt;div class="menu_options col-xs-6"&gt;&lt;div&gt;{icon}&lt;/div&gt;&lt;h3&gt;part3&lt;/h3&gt;&lt;/div&gt;
      &lt;div class="menu_options col-xs-6"&gt;&lt;div&gt;{icon}&lt;/div&gt;&lt;h3&gt;part4&lt;/h3&gt;&lt;/div&gt;
    &lt;/div&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>I want to put <code>{icon}</code> in the top of <code>partN</code> <em>(not next to each <code>partN</code>)</em>. how can I do that? As you know, both <code>&lt;div&gt;</code> and <code>&lt;h3&gt;</code> has <code>block</code> display. But I really don't know why they are next to each other. Anyway, how can I put them underneath each other?</p>