@keyframes rocket {
  0% {
    transform translateY(0)
    opacity 1;
  }
  45% {
    transform translateY(-3.2rem)
    opacity 0;
  }
  55% {
    transform translateY(3.2rem)
    opacity 0;
  }
  100% {
    transform translateY(0)
    opacity 1;
  }
}

.totop
  position relative
  display inline-block
  overflow hidden
  cursor pointer
  rounded-circle(3.2rem)
  background-color froth-light
  line-height 3rem
  &:hover > i {
    animation rocket .3s ease-in-out
  }