property controlling spacing in nav menu wp_list_categories – oulipo theme

Using the wp_list_categories() I’ve edited the code enough to get it to have a slide down effect for sub-categories. I’m trying to fine tune the css styling but am stuck with an expanse of space that shows up under each main child section, not between children sections (ie. between sub-categories and sub-sub-categories). I’m either missing a category or declaring it poorly.

<div id="main_nav">
    <ul class="menu">
	<li class="cat-item cat-item-1"><a href="https://url.com/maincat1">MainCat1</a>
<ul class='children'>
	<li class="cat-item cat-item-3"><a href="https://url.com/subcat1">SubCat1</a>

	<li class="cat-item cat-item-2"><a href="https://url.com/maincat2">MainCat2</a>
<ul class='children'>
	<li class="cat-item cat-item-4"><a href="https://url.com/subcat2">SubCat2</a>
	<ul class='children'>
	<li class="cat-item cat-item-5"><a href="https://url.com/subsubcat2">SubSubCat2</a>

And the css styling is:

[CSS moderated as per the Forum Rules. Please just post a link to your site.]

Any thoughts on why there is so much excess space below each child section? It is larger the more children there are.