For a basic "button" appearance, you can use an outset border on the links:
Code:
.categoryListBoxContents a br {display: none;}
.categoryListBoxContents a:link {
font-size: 1.2em;
font-weight: bold;
color: #FF0000;
padding: 0.3em;
background: #99aabb;
border: 3px outset #667788;
}
.categoryListBoxContents a:hover {
font-size: 1.2em;
font-weight: bold;
color: #000000;
}
.categoryListBoxContents {
float: left;
text-align: center;
}
You don't need the last rule, as it duplicates previous ones exactly.
A nicer rounded button that stretches to fit the text will take some more complex CSS.
A button image that is the same for all subcat links can be applied to
.categoryListBoxContents {
as a background, with no-repeat and center center positioning.