In this case, you can use method closest() or parent(). Here is an example using method closest().

Method closest() target a parent of any level relative to a child.

Method parent() only target the first level parent.

This is a jQuery solution:

$('li.selected').closest('ul').css('background', 'green');

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

<ul class="myul">
    <li>Button1</li>
    <li>Button2</li>
    <li class="selected">Button3</li>
    <li>Button4</li>
</ul>

<ul class="myul">
    <li>Button5</li>
    <li>Button6</li>
    <li>Button7</li>
    <li>Button8</li>
</ul>

This would be a job for the "has" selector in CSS. Unfortunately, as of this writing, there's almost no browser support for it. Safari Technology Preview "cutting edge" browser has support, and that's just about it.

https://caniuse.com/?search=has

You can search for "css parent selector" to see how this has been a longstanding request among many web developers.