_mixins.scss

@mixin make-grid-columns($cols: $cols-all) {
  // Common styles for all sizes of grid columns, widths 1-12
  @debug #{$cols};
  #{$cols} {
    position: relative;
    // Prevent columns from collapsing when empty
    min-height: 1px;
    // Inner gutter via padding
    padding-left:  ($grid-gutter-width / 2);
    padding-right: ($grid-gutter-width / 2);
  }
}