Going from One Third Columns down to One Half Columns on Mobile Size?

I am trying to use the columns shortcode and I’m using the one_third shortcode on desktop, then it wraps nicely to mobile. But I would really like it to go down to two on tablet size, I have modified some of the CSS for this but I can’t seem to get it right. One of my column items always stays to the left. Any solution for this? Thank you