Flex Grid Mixin

flexgrid.less

// Uses Flexbox to create grid with container's direct descendant elements
.flex-grid(@columns: 2, @margin: @indent-md) {

    @total-margin: (@columns - 1) * @margin;
    @first-column-offset: @columns + 1;

    .flex();
    .flex-wrap(wrap);

    > * {
        box-sizing: border-box;
        .flex-justify-content(space-between);
        width: ~'calc( ( 100% -'@total-margin~')/'@columns~')';

        &:not(:nth-child(@{columns}n + 1)) {
            margin-left: @margin;
        }

        &:nth-child(n + @{first-column-offset}) {
            margin-top: @margin;
        }
    }

    @media screen and (max-width: @screen-md) {
        > * {
            width: 100%;

            &:not(:last-child) {
                margin-bottom: @margin;
            }

            &:not(:nth-child(@{columns}n + 1)),
            &:nth-child(n + @{first-column-offset}) {
                margin-top: 0;
                margin-left: 0;
            }
        }
    }
}