Great! If you really want to vertically align the button based on the height of the left column, one option is to use JS or jQuery. So, first get the height of the left column (two_thirds). Then, set the top property of the right column (one_third last) equal to heightOfLeftColumn/2. Next, apply the transform:translateY(-50%) property to the right column. Finally, remember to do those changes only when your columns aren’t stacked.
If you want to avoid using JS though, you could also use flexbox.