• HTML
• CSS

HTML

<table class="table auto-count">
    <thead>
        <tr>
            <th>Número</th>
            <th>Descripción</th>
            <th>Adicional</th>
        </tr>
    </thead>
    <tbody>
        <tr>
            <td align="center"></td>
            <td>Aquí ira mi descripción</td>
            <td>...</td>
        </tr>
        <tr>
            <td align="center"></td>
            <td>Aquí ira mi descripción</td>
            <td>...</td>
        </tr>
        <tr>
            <td align="center"></td>
            <td>Aquí ira mi descripción</td>
            <td>...</td>
        </tr>
        <tr>
            <td align="center"></td>
            <td>Aquí ira mi descripción</td>
            <td>...</td>
        </tr>
    </tbody>
</table>

CSS

table
{
    border-collapse:collapse;
}
table tr>th,table tr>td{
    padding:1em;
}
table.auto-count
{
    counter-reset: rowNumber;
}
table.auto-count>thead{
    background:#a2d9ce;
}
table.auto-count>tbody{
    background:#f8f9f9;
}
table.auto-count>tbody>tr
{
    counter-increment: rowNumber;
}

table.auto-count>tbody>tr>th:first-child::before,
table.auto-count>tbody>tr>td:first-child::before
{
    content: counter(rowNumber);
}