Sass grid mixin

_grid.scss

// Demo & documentation : https://codepen.io/davidpollet/pen/wrxero
$grid-gutter-width : 1rem !default;
@mixin grid-item-per-row($items-per-row, $grid-gutter : $grid-gutter-width) {
  $grid-gutter-unitless : strip-unit($grid-gutter);
  width: 100 / $items-per-row - $grid-gutter-unitless * 1%;
  width: calc((100% / #{$items-per-row}) - #{$grid-gutter});
}

@mixin grid-gutter($grid-gutter: $grid-gutter-width) {
  $grid-gutter-unitless : strip-unit($grid-gutter);
  margin-left: $grid-gutter-unitless * 1%;
  margin-left: calc(#{$grid-gutter} * 1);
}