tml">
<p>There should be three lines below. The middle line should have a yellow
  background that takes up about 50% of the viewport width (but otherwise be
  exactly like the two others, i.e. no extra height or anything like that).</p>
A B C D E F G
<div style="writing-mode:vertical-rl; background:yellow;">
  <div style="writing-mode:horizontal-tb; width:50%;">
    A B C D E F G
  </div>
</div>
A B C D E F G
