CSS selector to get deepest element of specific class in the HTML tree

I've got a a bunch of DIV elements in my HTML, several of which have their class attribute set to "rowsLayout". Some of these rowsLayout DIVs can be nested inside one another. I want to define a CSS selector that only targets the deepest DIVs in those nestings. That is, I don't want any of the rowsLayout DIVs that contain any other rowLayout DIVs.

<div id="a" class="rowsLayout">
  <div id="b" class="rowsLayout" />
  <div id="c" class="rowsLayout">
    <div id="d" class="rowsLayout" />
  </div>
</div>
<div id="e" class="rowsLayout" />

With this structure, I want a selector that will target b, d, and e.

Can this be done?

You can use the jQuery selector .rowsLayout:not(:has(.rowsLayout)).

However, for performance reasons, this is not possible in CSS.

Your selector depends on the children (or lack thereof) of the elements that you target.
CSS is designed so that an element's selectors can always be resolved before the element's children exist; this allows CSS to be applied as a document loads.