nth-child of
by cambraca
HTML
<ul>
<li>One</li>
<li>Two</li>
<li class="hidden">Three</li>
<li>Four</li>
<li>Five</li>
<li>Six</li>
<li>Seven</li>
</ul>
CSS
li:nth-child(2n of :not(.hidden)) {
background-color: lightgrey;
}
li.hidden {
display: none;
}