This example will produce a three column layout with a 25%/58.34%/16.66% (l3, l7, l2) split on large screens, 50%/25%/25% (m6, m3, m3) split on medium screens and a 33.3%/33.3%/33.3% (s4, s4, s4)split on small screens:
l3 m6 s4
l7 m3 s4
l2 m3 s4
Inside a container: