HTML Demo: <col>

<table>
    <caption>Superheros and sidekicks</caption>
    <colgroup>
        <col>
        <col span="2" class="batman">
        <col span="2" class="flash">
    </colgroup>
    <tr>
        <td> </td>
        <th scope="col">Batman</th>
        <th scope="col">Robin</th>
        <th scope="col">The Flash</th>
        <th scope="col">Kid Flash</th>
    </tr>
    <tr>
        <th scope="row">Skill</th>
        <td>Smarts</td>
        <td>Dex, acrobat</td>
        <td>Super speed</td>
        <td>Super speed</td>
    </tr>
    <tr>
        <th scope="row">Weapon</th>
        <td>Martial, gadgets</td>
        <td>Martial, gadgets</td>
        <td>Martial</td>
        <td>Martial</td>
    </tr>
</table>

.batman {
    background-color: #d7d9f2;
}

.flash {
    background-color: #ffe8d4;
}

caption {
    padding: 8px;
    caption-side: bottom;
}

table {
    border-collapse: collapse;
    border: 2px solid rgb(100, 100, 100);
    letter-spacing: 1px;
    font-family: sans-serif;
    font-size: .7rem;
}

td,
th {
    border: 1px solid rgb(100, 100, 100);
    padding: 10px 10px;
}

td {
    text-align: center;
}

Output