title: Make flex items wrap to existing lines, not new lines
body: <p>I'm trying to style a table (I can't change the HTML) as a flexbox that flows responsively without leaving gaps.</p>
  
  <p>My starting table on wide screens</p>
  
  <pre><code>+---+---+---+---+
  | A | B | C | D |
  +---+---+---+---+
  | w | x | y | z |
  +---+---+---+---+
  </code></pre>
  
  <p>When I narrow the screen this is what I get:</p>
  
  <pre><code>+---+---+---+
  | A | B | C |
  +---+---+---+
  | D | 
  +---+---+---+
  | w | x | y |
  +---+---+---+
  | z | 
  +---+
  </code></pre>
  
  <p>What I'd like:</p>
  
  <pre><code>+---+---+---+
  | A | B | C |
  +---+---+---+
  | D | w | x |
  +---+---+---+
  | y | z |   |
  +---+---+---+
  </code></pre>
  
  <p>Here is the CSS I have so far: </p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-css lang-css prettyprint-override"><code>/* Relevant flexbox stuff */
  .respondable {
    display: flex;
  }
  .respondable tr {
    display: flex;
    flex-direction: row;
    flex-wrap: wrap
  }
  
  /* Pretty stuff */
  .respondable {
    border-collapse: collapse;
  }
  .respondable td {
    border: 1px solid black;
    border-collapse: collapse;
    width: 100px;
    text-align: center;
    background: #eeeeee
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>Narrow screen to see D jump onto line of its own
  &lt;table class="respondable"&gt;
    &lt;tr&gt;
      &lt;td&gt;A&lt;/td&gt;
      &lt;td&gt;B&lt;/td&gt;
      &lt;td&gt;C&lt;/td&gt;
      &lt;td&gt;D&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
      &lt;td&gt;w&lt;/td&gt;
      &lt;td&gt;x&lt;/td&gt;
      &lt;td&gt;y&lt;/td&gt;
      &lt;td&gt;z&lt;/td&gt;
    &lt;/tr&gt;
  &lt;/table&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p><a href="https://jsfiddle.net/h9s7nkar/" rel="nofollow noreferrer">https://jsfiddle.net/h9s7nkar/</a></p>