Highlight Currently Selected Category Background

[gjh42]

There is a class added to categories in the currrently selected path that can be used to do what you want. The Classic template uses this to make the current category path bold:

SPAN.category-subs-parent {
font-weight: bold;
}
SPAN.category-subs-selected {
font-weight: bold;
}

Even though your Template Monster template has changed the categories menu structure (with good reason for a change:), you can still use those classes.