.class:nth-child(1) {
background-position-y:0%;
}
.class:nth-child(2) {
background-position-y:25%;
}
.class:nth-child(3) {
background-position-y:50%;
}
for n in (1..3)
.class:nth-child(n)
background-position-y (n - 1) * 25 \%
.class:nth-child(n) {
background-position-y: 0 %;
}
.class:nth-child(n) {
background-position-y: 25 %;
}
.class:nth-child(n) {
background-position-y: 50 %;
}
for $n in (1..3)
.class:nth-child({$n})
background-position-y ($n - 1) * 25%