从指定的宽度扩展div基数的宽度，而不调整表td的大小

Question

下面是我的代码片段，我试图实现的是在给定宽度上扩展宽度基数（600px，因为你可以看到有一个宽度为600px的div）而没有调整其容器的大小（td，你可以看到td正在扩展，也是基于它的子宽度为600px，我不想要）。我希望宽度为600px的div与在aug和sep下的td容器对齐，有没有办法实现呢？

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#table_roadmap th, #table_roadmap td {
  padding: 8px;
  border: 1px solid rgba(0, 0, 0, 0.1);
}

#table_roadmap thead {
  background-color: #ededed;
}

#table_roadmap th:first-child {
  background-color: #40b649;
  color: #ffffff;
}

#table_roadmap th {
  text-align: center;
  font-weight: 700;
}

#table_roadmap tbody tr td:first-child {
  background-color: #40b649 !important;
  color: #ffffff !important;
  font-weight: 700 !important;
  width: 200px !important;
}

#table_roadmap tbody td {
  height: 100px;
  width: 300px;
}

#table_roadmap .roadmap_card_main {
  padding: 3px 5px;
  font-size: 10px;
  margin: 3px;
  background-color: green;
  color: #fff;
}

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<table id="table_roadmap" class="center" cellpadding="0" cellspacing="0">
  <thead>
    <th>Projects</th>
    <th>Jan</th>
    <th>Feb</th>
    <th>Mar</th>
    <th>Apr</th>
    <th>May</th>
    <th>Jun</th>
    <th>Jul</th>
    <th>Aug</th>
    <th>Sep</th>
    <th>Oct</th>
    <th>Nov</th>
    <th>Dec</th>
  </thead>
  <tbody>
  <tr>
    <td>Project 1
    <td>test</td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
    <td>
      <div class="roadmap_card_main extend clear bg_green">Card title test 1</div>
      <div class="roadmap_card_main extend clear bg_green" style="position: relative; width: 600px;">Card title test 1</div>
    </td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
  </tr>
  <tr>
    <td>Project 2</td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
    <td>
      <div class="roadmap_card_main extend clear bg_green">Card title test 1</div>
    </td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
  </tr>
  <tr>
    <td>Project 3
    <td>test</td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
    <td>
      <div class="roadmap_card_main extend clear bg_green">Card title test 1</div>
    </td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
  </tr>
  <tr>
    <td>Bug Checking</td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
    <td>
      <div class="roadmap_card_main extend clear bg_green">Card title test 1</div>
    </td>
    <td>test</td>
    <td>test</td>
    <td>test</td>
  </tr>
  </tbody>
</table>

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