JSFiddle - React, Tailwind, and code Playground

HTML

<table id="table1">
  <thead>
    <tr>
      <th>Pořadí</th>
      <th>Jméno</th>
      <th>Věk</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td></td>
      <td>davidek</td>
      <td>169</td>
    </tr>
    <tr>
      <td></td>
      <td>davidek</td>
      <td>169</td>
    </tr>
    <tr>
      <td></td>
      <td>Honza</td>
      <td>86</td>
    </tr>
    <tr>
      <td></td>
      <td>Honza</td>
      <td>86</td>
    </tr>
  </tbody>

CSS

table#table1 {
    counter-reset: rowNumber;
}

table#table1 tbody tr {
    counter-increment: rowNumber;
}

table#table1 tbody tr td:first-child::before {
    content: counter(rowNumber);
}