JSFiddle - React, Tailwind, and code Playground

HTML

<table style="width:100%">
  <tr>
    <th>Column1</th>
    <th>Column2</th>		
    <th>Column3</th>
  </tr>   
  <tr>
    <td>Jill</td>
    <td>Smith</td>		
    <td>50</td>
  </tr>
  <tr>
    <td>Eve</td>
    <td>Jackson</td>		
    <td>94</td>
  </tr>
  <tr>
    <td>John</td>
    <td>Doe</td>		
    <td>80</td>
  </tr>
</table>

CSS

.col-md-1{
    background-color: blue;    
}

JavaScript

$("table tr th:nth-child(1)").addClass("col-md-1");