You won't find it, that is the problem, it's using the default value for that property which I think is
I'm not one for using frameworks, but I think it is usual practice to put any customisations into a separate css, so as not to "muddy" the original. That should help you not break it and make updates easier.
Two ways: you could add a rule:-
vertical-align: top; /* or middle if you like */
But modifying the frameworks class may break how it works, so the alternative is a new class, called whatever you like:-
Which would require the class adding to the html also.
<div class="col v-top">