I know this question was asked many times, but it's still unfigurable for me. Anyway I have a code like this:
<div id="header">
Here are many different div's with various position (relative, absolute, static, etc).
</div>
<div id="content">
  <div class="row">
    <div class="inner">
      <div class="upper">
         Some dummy content
      </div>
      <div class="lower">
      </div>
    </div>
  </div>
</div>
Now, how can I set for example .upper div to fit into the window, since I have no idea what's the height of header?