::v-deep usage as a combinator has been deprecated. Use :deep() instead.
原因新的vue3.0 单文件规范::v-deep写法已经被废弃了
修改成 如下写法，不要加空格
//报错
<style scoped>
::v-deep .demo{
background: yellow;
}
</style>//正确
<style scoped>
:deep(.demo){
background: yellow;
}
</style>