isudet.html#blockwidth"/>
  <style type="text/css">
   .test { border-left: 2em solid; padding-left: 0; width: 3em; padding-right: 0; border-right: 2em solid; box-sizing: border-box; }
   .control { border-left: none; padding-left: 0; width: 4em; padding-right: 0; border-right: none; }
   .body div { background: navy; border-color: navy; height: 1em; }
  </style>
 </head>
 <body class="body">
  <p>There must be a perfectly rectangular blue box below.</p>
  <div class="test"></div>
  <div class="control"></d