<!DOCTYPE html>
<html>
  <head>
    <script>
      function test() {
        var elem = document.getElementById("test");
        elem.style.width = "350px";
      }
    </script>
  </head>
  <body onload="test()">
    <iframe id="test" style="width:400px;"
            src="data:text/html,
                 <html>
                   <style>
                     html { writing-mode:vertical-rl; }
                     div { writing-mode:initial; position:absolute;
                           right:0; padding:5px; }
                   </style>
                   <div>This text should NOT be cut off</div>">
    </iframe>
  </body>
</html>