.fade-enter-active, .fade-leave-active {
transition: opacity 3s;
}
.fade-enter, .fade-leave-to /* .fade-leave-active below version 2.1.8 */ {
opacity: 0;
}
<transition
v-on:before-enter="beforeEnter"
v-on:enter="enter"
v-on:after-enter="afterEnter"
v-on:enter-cancelled="enterCancelled"
v-on:before-leave="beforeLeave"
v-on:leave="leave"
v-on:after-leave="afterLeave"
v-on:leave-cancelled="leaveCancelled"
>
<!-- ... -->
</transition>