<!DOCTYPE html>
<html>
  <head>
    <title>Column clipping</title>
    <style>
      body {
        width: 450px;
        color: black;
        background: white;
      }
    
    .mc { border:10px solid green;height:100px; box-sizing:border-box }
    .rect { float:left; border-right:10px solid green; width:115px; height:80px; box-sizing:border-box; }
    </style>
  </head>
  <body>
    <p>There should be a rectangle with a solid 10px thick green border below, and no red.</p>
    <div class="mc">
         <div class="rect"></div>
        
        <div class="rect"></div>
        
    </div>
  </body>
</html>