Responsive Grid Question

Hey people,

Lets say I have a div class=“col-25” on a portrait phone, I want this to be div class=“col-50” on a tablet in landscape for example. Can anyone explain to me how I might do this? Can’t I do something like this: div class=“col-50 responsive-sm-25” (I know I can’t do this, but you get the picture)

Thanks-
MB