JSFiddle - React, Tailwind, and code Playground

HTML

<h1>Deelnemers:</h1>
<table>
    <tr>
        <th colspan="5">Blok 2</th>
    </tr>
    <tr>
        <th>26-05-13</th>
        <th>09-06-13</th>
        <th>23-06-13</th>
        <th>Totaal</th>
        <th>Uitslag</th>
    </tr>    
</table>

CSS

table, th, td {
    border: 1px solid black;
    border-collapse: collapse;
}