scss-library/components/00_Global/_elementAmount.scss

@mixin RV-Utils__ElementAmount($-up-to: 20) {
    @for $i from 1 through $-up-to {

        *:first-child:nth-last-child(#{$i}),
        *:first-child:nth-last-child(#{$i})~* {
            @content($i);
        }
    }
}