the problem stems from the fact that in your code the H2s are DECEDENTS , NOT CHILDREN, of the DL. As only DT’s and DDs can be children of DLs, you may acieve what you are going after by targeting the DTs first… EXCEPT that the NTH:CHILD selector selects , well… the Nth CHILD, that is the Nth tag within the parent, regardless of type. For example , the second child would actually be the first DD, the third would be the following tag(second DT) and so forth.
You may achieve what you are going after by using Nth of type, like this:
I’d also be asking what makes that a definition list and what makes those H2’s? They don’t appear to be starting new sections, and you have empty terms…
though that they are “slides” is setting off my ‘pointless space-waster’ sense.