Flexbox with non block children

<div class="container">

  <div class="flex-parent">

    <span class="flex-child-label">Inbox</span>

    <span class="flex-child">1</span>

  </div>

  <div class="flex-parent">

    <span class="flex-child-label">Sent</span>

    <span class="flex-child">2</span>

  </div>

  <div class="flex-parent">

    <span class="flex-child-label">More</span>

    <span class="flex-child">3</span>

  </div>

<div>