title: Why the button with a fixed height can't align perfect with other buttons when there's something in it but not using up its height?
body: <p>There are 6 buttons, the second one has something inside. But I defined all the buttons a fixed height and the inside content is not using up the room at all. Why it's still not in the expected position?</p>
  <p>Please take a look at this simple 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>button {height:60px;width:50px;border:1px solid #000;box-sizing:border-box}
  button span {display:block;color:grey; font-size:9px}</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;button&gt;1&lt;/button&gt;
  &lt;button&gt;2&lt;span&gt;2.1&lt;/span&gt;&lt;/button&gt;
  &lt;button&gt;3&lt;/button&gt;
  &lt;button&gt;4&lt;/button&gt;
  &lt;button&gt;5&lt;/button&gt;
  &lt;button&gt;6&lt;/button&gt;</code></pre>
  </div>
  </div>
  </p>