for absolutely positioned elements, in the presence of dynamic changes to 'width' of the containing block.">
<style>

html {
  writing-mode: vertical-rl;
  direction: rtl;
  overflow: hidden;
}

#container {
  position: absolute;
  top: 0;
  left: 0;
  width: 100px;
  height: 200px;
  background: yellow;
}

#abspos {
  position: absolute;
  bottom: 80px;
  left: 70px;
  top: 80px; /* ignored */
  width: 10px;
  height: 10px;
  background: fuchsia;
}

</style>

<div id="container">
  <div id="abspos"></div>
