<!DOCTYPE html>
<html>
<head>
<style>
.slr {
   writing-mode: sideways-lr;
}
</style>
</head>
<body>
  <div style="height:0px;width:0px;overflow:visible">
    <div style="height:100px;width:120px;background:rgba(0,255,0,0.8);display:inline-block;margin-top:calc(100vh - 316px);"></div>
  </div>
  <div style="height:0px;width:0px;overflow:visible">
    <div style="height:100px;width:150px;background:rgba(255,0,0,0.8);display:inline-block;margin-top:calc(100vh - 216px);"></div>
  </div>
  <div class="slr" style="background:silver; height: calc(100vh - 16px);">
    <div style="height:100px;">This text should appear BELOW the red and green blocks.</div>
  </div>
</body>
</html>