Broadcast theme - Customizing the link list drop down menu

[robprl]

Site: https://u9a0gjwtkkrv74cb-59737833631.shopifypreview.com

My link lists for my menu are too long and I'd like to break it up into two or three columns under the single headers, "Fabric" and "Colors". I'm using the Broadcast theme. Apps don't seem helpful for this customization.

I tried to use the following in theme.liquid but it didn't work.
<script>
var maxRows = 6;
$('.site-nav ul.site-nav__dropdown-f6c27efeea36e69852a48e57e2d29ded').each( function() {
var totalRows = $(this).grandchildren('li').length;
var columns = Math.ceil(totalRows/maxRows).toString();
$(this).css({
"-webkit-column-count": 3,
"-moz-column-count": 3,
"column-count": 3,
});
});
</script>

Any suggestions?

An example of what I want is nuagedesigns.com. Hover over "Linens and tabletop" and see the two columns under "Browse by Collection"