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>