bootstrap 4

by Eugen Sunic

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js"></script>
<table class="table table-bordered table-hover">
  <tr>
    <td>cell10</td>
    <td>cell 11</td>
    <td>cell 11</td>
    <td>cell 11</td>
    <td>cell 11</td>
  </tr>
  <tr>
    <td colspan="100%">
      <table class="table">
        <tr>
          <td>Nested 1a</td>
          <td>Nested 2a</td>
          <td>Nested 3a</td>
        </tr>
      </table>
    </td>
  </tr>
</table>

CSS

.container {
  margin-top: 20px;
  margin-bottom: 20px;
}