如何标记月历中的所有日期

<div class="calendar">
  <table>
    <thead>
      <tr>
        <th>Sun</th>
        <th>Mon</th>
        <th>Tue</th>
        <th>Wed</th>
        <th>Thu</th>
        <th>Fri</th>
        <th>Sat</th>
      </tr>
    </thead>
    <tbody>
      <tr>
        <td></td>
        <td></td>
        <td></td>
        <td></td>
        <td></td>
        <td></td>
        <td>1</td>
      </tr>
      <!-- ... continue the rest of the days -->
    </tbody>
  </table>
</div>

.calendar {
  width: 100%;
}

table {
  width: 100%;
  border-collapse: collapse;
}

th, td {
  padding: 10px;
  text-align: center;
  border: 1px solid #ccc;
}

th {
  background-color: #f2f2f2;
}

td {
  cursor: pointer;
}

td.marked {
  background-color: #ffc;
}