title: How do I vertical center a label in a div?
body: <p>I have a <code>div</code> with a height of <code>30px</code>.</p>
  <p>I want to add plain text to this <code>div</code>. How can I make the plain text appear on the center of my div?
  i.e, the text will be shown <code>15px</code> under the top of the <code>div</code>.</p>
  <p>I tried a label with <code>margin-top: 15;</code> but it didn't work.</p>