Bootstrap Grid hide the side when small

examples/bootstrap/responsive_grid_hide_margin.html

<html>
  <head>
  <title>Hide side</title>
  <meta name="viewport" content="width=device-width" />
  <link href="css/bootstrap.min.css" rel="stylesheet" />

  <style>
  .left {
      background-color: red;
  }
  .main {
      background-color: lightblue;
  }
  .right {
      background-color: lightgreen;
  }
  </style>
  </head>
  <body>
    <div class="container-fluid">

      <div class="row">
        <div class="col-xs-12 col-md-9 main">.col-xs-12 .col-md-9</div>
        <div class="col-md-3 visible-md-block visible-lg-block right">.col-md-3</div>
      </div>
      <hr>

    </div>  
  </body>
</html>