<style>
.container > div {
  background-color: green;
  width: 100px;
  display: inline-block;
}

.horizontal {
  height: 100px;
}

.vertical {
  writing-mode: vertical-rl;
  overflow-y: scroll;
  border: 50px solid green;
}
</style>
<!-- Do not take (non-visible) scrollbar into account while aligning the empty vertical container -->
<div class=container><div class=horizontal></div><div class=vertical></div></div>