The trick was to add position: relative to the associated CSS definition. Here's how I got the border to show up on hover:
.category_item_title a { text-decoration: none; color: #3C2517; } .category_item_title a:hover { border-bottom: 4px dotted #3C2518; position: relative; /* ADDED THIS! */ }Once I added position: relative on hover, it displayed perfectly. Why? I have no idea. But it works, and I am happy.