JSFiddle - React, Tailwind, and code Playground

HTML

<table id="display-tag">
<thead>
    <tr>
        <th>
            Firstname
        </th>
        <th>
            Lastname
        </th>
    </tr>
</thead>
<tbody>
    <tr>
        <td>Bob</td>
        <td>Test</td>
    </tr>
    <tr>
        <td>Jane</td>
        <td>Test</td>
    </tr>
</tbody>
</table>

CSS

th, td {
  padding:5px;  
  border: solid 1px grey;    
}

JavaScript

$('#display-tag > thead').prepend('<tr><th colspan="2">heading</th></tr>');