JSFiddle - React, Tailwind, and code Playground

HTML

<table>
    <tr><td>Data</td></tr>
    <tr><td>Data</td></tr>
    <tr><td>Data</td></tr>
    <tr><td>Data</td></tr>
    <tr><td>Data</td></tr>
    <tr><td>Data</td></tr>
    <tr><td>Data</td></tr>
    <tr><td>Data</td></tr>
    <tr><td>Data</td></tr>         <tr><td>Data</td></tr>
</table>

CSS

td {
  padding: 5px;
  background: #ddd;
  border: 1px solid #aaa;
}

tr.dark td {
  color: #fff;
  background: #000;   
}

JavaScript

$('table tr').slice(-2, -1).addClass('dark');