css3 &

.z-dropdown-menu {
  background-color: rgba(4, 26, 101, 0.9);
  border: 1px solid #3e9edd;
  z-index: 99999;
  &__item {		// & 代表.z-dropdown-menu
    font-size: 1.2rem;
    &:hover {		// & 代表.z-dropdown-menu_item
      font-size: 1.6rem;
    }
  }
}