小编Joa*_*ska的帖子

th:last-child {
   width: calc( (100% - 30px)/12 + 30px );
}
table, tr {
width:100%;
border: 1px solid black;
height:10px;
}
th {
  border-right: 1px solid black;
  width: calc( (100% - 30px)/12 );
}

<table>
<thead>
  <tr>
    <th>Column 1</th>
    <th>Column 2</th>
    <th>Column 3</th>
    <th>Column 4</th>
    <th>Column 5</th>
    <th>Column 6</th>
    <th>Column 7</th>
    <th>Column 8</th>
    <th>Column 9</th>
    <th>Column 10</th>
    <th>Column 11</th>
    <th>Column 12</th>
  </tr>
</thead>
<tbody>
 <tr>
    <td>Row 1</td>
    <td>Row 2</td>
    <td>Row 3</td>
    <td>Row 4</td>
    <td>Row 5</td> …