When using only mixins to make the columns, without a mixin at the mobile base level, the div doesn't have the styles that it would when used in HTML: position: relative; min-height: 1px; padding-left: 15px; padding-right: 15px;

gistfile1.less

.left {
  // What goes here?
  @media(min-width: @screen-tablet) {
    .make-sm-column(6);
  }
  @media(min-width: @screen-desktop) {
    .make-md-column(3);
  }
  @media(min-width: @screen-large-desktop) {
    .make-lg-column(9);
  }
}

.right {
  // What goes here?
  @media(min-width: @screen-tablet) {
    .make-sm-column(6);
  }
  @media(min-width: @screen-desktop) {
    .make-md-column(9);
  }
  @media(min-width: @screen-large-desktop) {
    .make-lg-column(3);
  }
}