Untitled

<!DOCTYPE html>
<html lang="en">
<head>
  <title>Bootstrap Example</title>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/css/bootstrap.min.css">
  <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
  <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.4.1/js/bootstrap.min.js"></script>

  <style>
    .page-container {
      margin: 0;
      padding: 0;
      position: relative;
    }
    .page-content-wrapper {
      float: left;
      width: 100%;
    }
    .page-content {
      margin-left: 235px;
      margin-top: 0;
      padding: 25px 20px 10px;
    }
  </style>
</head>
<body>

  <div class="page-container">
    <div class="page-sidebar-wrapper">
      <h1>SIDEBAR</h1>
    </div>
    <div class="page-content-wrapper">
      <div class="page-content">
        <h1>CONTENT</h1>
        <div class="row">
          <div class="col-lg-8 col-md-12 col-md-offset-2 col-sm-12 col-xs-12">
            <h5>This box should be a 12 grids size on my laptop and 8 grids size on my desktop.</h5>
          </div>
        </div>
      </div>
    </div>
  </div>

</body>
</html>