Выбрать 3 элемента через 3 - Вопросы по CSS

.card:nth-child(n + 3).card:nth-child(-n + 5)

.card:nth-child(n + 8).card:nth-child(-n + 10)

.card:first-child + .card + .card + .card,
.card:first-child + .card + .card + .card + .card,
.card:first-child + .card + .card + .card + .card + .card {
...
}

img:first-child + img + img + img, 
img:first-child + img + img + img + img, 
img:first-child + img + img + img + img + img {
    opacity: 0.25;
}