Susu responsive grid

gistfile1

$total-columns: 4;

#main {
  @include container(4,30em 12); // at min-width 30-em we establish a 12-column grid
  section.nav {
    @include span-columns(4); // by default we have 4 columns
    @include at-breakpoint(30em 12) { // at 30em we want 12 columns
      @include span-columns(12); // now we have 12
  }
}