<p>Element with no content:</p>
<div></div>

<p>Element with comment:</p>
<div><!-- Simple Comment --></div>

<p>Element with whitespace:</p>
<div>    </div>

<p>Element with nested empty element:</p>
<div><p></p></div>

div:empty {
    outline: 2px solid deeppink;
    height: 1em;
}