vue自定义transition样式前缀名

<transition name="pretty">
    <div class="img" v-if="flag">
        <img :src="img" alt="" width="150">
    </div>
</transition>

.pretty-enter,
.pretty-leave-to {
    opacity: 0;
    transform: translateY(200px);
}

.pretty-enter-active,
.pretty-leave-active {
    transition: all 1.5s ease;
}