ul {
  border: 1px solid #ccc;
  margin: 20px;
  padding: 10px 10px 10px 30px;
}

li:only-of-type {
  color: red;
}

<ul>
  <li>I'm all alone!</li>
</ul>  

<ul>
  <li>We are together.</li>
  <li>We are together.</li>
  <li>We are together.</li>
</ul> 

p:only-of-type {
  color: red;
}
<div class="box">
	<div>
  <p>I'm the only paragraph element in this div.</p>  
  <ul>
    <li>List Item</li>
    <li>List Item</li>
  </ul>  
</div>

<div>
  <p>There are multiple paragraphs inside this div.</p>  
  <p>Yes there are.</p>  
  <ul>
    <li>List Item</li>
    <li>List Item</li>
  </ul>  
</div>
</div>