title: Change display of sibling by his brother children count
body: <p>Hi i have the following html</p>
  
  <pre><code>&lt;div&gt;
      &lt;div class='brother1'&gt;
        HELLO
         &lt;div class='item'&gt;One&lt;/div&gt;
         &lt;div class='item'&gt;Two&lt;/div&gt;
         &lt;div class='item'&gt;Three&lt;/div&gt;
         &lt;div class='item'&gt;Seven&lt;/div&gt;
      &lt;/div&gt;
  
      &lt;div class='brother2 button'&gt;
          BUTTON
      &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>I want to set button to be invisible if the amount of items(One,Two,Three...) is bigger that 3.<br>
  But if the amount is less then 3 i want the button to be visible.</p>
  
  <p>Is this possible using <strong>css only?</strong></p>
  
  <p>If this is not possible how would you change the html structure to achieve the same behavior?</p>
  
  <p>Thanks.</p>