1.在/assert目录下建立一个page-transletion.css文件，里面包含过渡动画内容，内容如下：
```
.page-enter-active, .page-leave-active {
transition: opacity .5s;
}
.page-enter, .page-leave-active {
opacity: 0;
}
```
2.在nuxt.config.js中配置：
```
css: [
'assets/page-transletion.css'
]
```
