@bg-img-01: url("/website/image/theme_common.image_content_11");
@bg-img-02: url("/website/image/theme_common.image_content_09");
@bg-img-03: url("/website/image/theme_common.image_content_10");
@bg-img-04: url("/website/image/theme_common.image_content_12");

.o-generate-bg-img-options(4);
.o-generate-bg-img-options(@n, @i: 1) when (@i =< @n) {
    .bg-img-0@{i} {
        background-image: ~"@{bg-img-0@{i}}";
        background-size: cover;
        background-position: center center;
    }
    .o-generate-bg-img-options(@n, @i + 1);
}