LayoutTests/fast/ruby/simple-overhang-vertical-lr-expected.html

<style>
rt {
 font-size: 20px;
 color: transparent;
}

.container {
  font-family: Ahem;
  font-size: 20px;
  writing-mode: vertical-rl;
}
</style>
<div class=container>X<ruby>base<rt>annotation</rt></ruby>X</div>