@mixin col($col, $sum, $gap: 1em, $align: top) {
  width: 100%;
  display: inline-block;
  box-sizing: border-box;
  float: left;
  padding: 0 15px;

  @media only screen and (min-width: 768px) {
    width: percentage($col/$sum);
    vertical-align: $align;
  }
}