Set min-width either by content or 200px (whichever is greater) together with max-width

Solution 1:

The problem is that flex: 1 sets flex-basis: 0. Instead, you need

.container .box {
  min-width: 200px;
  max-width: 400px;
  flex-basis: auto; /* default value */
  flex-grow: 1;
}

.container {
  display: -webkit-flex;
  display: flex;
  -webkit-flex-wrap: wrap;
  flex-wrap: wrap;
}

.container .box {
  -webkit-flex-grow: 1;
  flex-grow: 1;
  min-width: 100px;
  max-width: 400px;
  height: 200px;
  background-color: #fafa00;
  overflow: hidden;
}
<div class="container">
  <div class="box">
    <table>
      <tr>
        <td>Content</td>
        <td>Content</td>
        <td>Content</td>
      </tr>
    </table>    
  </div>
  <div class="box">
    <table>
      <tr>
        <td>Content</td>
      </tr>
    </table>    
  </div>
  <div class="box">
    <table>
      <tr>
        <td>Content</td>
        <td>Content</td>
      </tr>
    </table>    
  </div>
</div>