Percentage widths, set your column size by restricting the .container
On larger screens, split larger column in two, then on smaller screens split them while still keeping the overall grid.
On larger screens, allow smaller columns to site beside other column but on smaller screens 'shunt' them down below its siblings.
On larger screens, allow smaller columns to site beside other column but on smaller screens 'shunt' them down below its siblings.
On larger screens, allow smaller columns to site beside other column but on smaller screens 'shunt' them down below its siblings.