title: Making a page centered as long as it does not overflow in CSS
body: <p>I have a web-page, which has a body that expands over time (by user clicks and such), that I want to be centered (vertically).</p>
  <p>I also want it to be scroll-able when the content exceeds the page's height (when it overflows), but then it has to be aligned to the top of the page.</p>
  <p>I want it to behave like this, and I want to achieve it with <code>flexbox</code>:</p>
  <p><a href="https://i.stack.imgur.com/Uql7N.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Uql7N.png" alt="Target Behavior" /></a></p>
  <p>Any ideas?</p>