<!DOCTYPE html>
<html class="slr">
<head>
<style>
.slr {
  writing-mode: sideways-lr;
  direction: rtl;
}
</style>
</head>
<body>
 <div>
  <div dir="ltr" style="inline-size:-moz-fit-content">
    <div style="height:300px">
      <div style="height:100px;width:120px;background:rgba(0,255,0,0.8);float:right;"></div>
    </div>
    <div style="height:200px">
      <div style="height:100px;width:150px;background:rgba(255,0,0,0.8);float:right;"></div>
    </div>
  </div>
  <div style="background:silver">
This text should appear BELOW the red and green blocks.
  </div>
 </div>
</body>
</html>