grid.scss

$grid-columns: 					12;
$grid-gutter: 					20px;
$base-grid: 					(columns: $grid-columns, margins: $grid-gutter);

@mixin span-col($column-span, $settings: $base-grid) {
    $grid-columns: map-get($settings, columns);
    $grid-width: 100;
    $grid-gutter: map-get($settings, margins);
    $width: ($grid-width / $grid-columns * $column-span);

    $column-total: ($grid-columns / $column-span);
    $newGutter: $grid-gutter - ($grid-gutter / ($column-total));
    
    margin-left: $grid-gutter;
    width: calc(#{$width}% - #{$newGutter});
}