JSFiddle - React, Tailwind, and code Playground

HTML

<table>
    <tr>
        <th>Mandag</th><td>08:00</td><td>09:00</td><td>10:00</td><td>11:00</td><td>12:00</td>
    </tr>
    <tr>
        <th>Tirsdag</th><td>08:00</td><td>09:00</td><td>10:00</td><td>11:00</td><td>12:00</td>
    </tr>
    <tr>
        <th>Onsdag</th><td>08:00</td><td>09:00</td><td>10:00</td><td>11:00</td><td>12:00</td>
    </tr>
    <tr>
        <th>Torsdag</th><td>08:00</td><td>09:00</td><td>10:00</td><td>11:00</td><td>12:00</td>
    </tr>
    <tr>
        <th>Fredag</th><td>08:00</td><td>09:00</td><td>10:00</td><td>11:00</td><td>12:00</td>
    </tr>
    <tr>
        <th>Lørdag</th><td>08:00</td><td>09:00</td><td>10:00</td><td>11:00</td><td>12:00</td>
    </tr>
    <tr>
        <th>Søndag</th><td>08:00</td><td>09:00</td><td>10:00</td><td>11:00</td><td>12:00</td>
    </tr>
</table>

CSS

.colored{
    background-color:black;
    color:white;
}

JavaScript

$("td").click(function(){
    $(this).toggleClass("colored");
});