.item:first-child,
.item:nth-child(3n+4) {
// 1,4,7,10...
}
.item:nth-child(3n+3) {
// 3,6,9,12...
}
.item:nth-child(3n+1) {
// 1,4,7,10...
}
:nth-child(3n) {
// 3, 6 ,9, 12
}
:nth-child(3n - 2) {
// 1 4 7 10
}
:nth-child(1),
:nth-child(4),
:nth-child(7),
:nth-child(10),
{
// 1 4 7 10
}