I added 2% to the left margin only.  This is because we wanted 2% margin between each element.  If both the left and right margins were set to 2%, it would be the proper distance away from the outer edges.  But if the left column's right margin is set to 2% and the right column's left margin is also set to 2%, suddenly you'd have 4% between the two.  And since we don't have that much room, it would instead just push the right column down beneath.