Cannot call mixins which are wrapped inside prefix-classes()

[tuanngo1993]

+prefix-classes("prefix-") {

mixin() {
margin-left 10px
}

.button {
mixin() // work well
}

}

.tooltip {
mixin() // does not work to call here
}

it is only able to call mixin from a selector wrapped by the same prefix-classes(). Do you guys know how to call such mixin from a selector outside?