[Bug Report] van-dropdown-menu incorrect offset of van-dropdown-item when places inside van-popup

[Looooooka]

Reproduction Link

https://codesandbox.io/s/vant-3-issue-template-forked-hhgzej?file=/src/App.vue

Vant Version

3.4.9

Describe the Bug

After trying to use the van-dropdown-menu(used the sample code in the documentation) inside a van-popup I can see the offset property of the drop down items is incorrect. it's getting it from the menubar's bottom position but it's way off (by like 600px vertically). If used outside the van-popup it display's under the menu as expected.

Reproduce Steps

drop van-dropdown-menu sample code from the documentation inside a van-popup

Device / Browser

Desktop (dev,beta,production version of edge as well as latest version of chrome)

[goo-yyh]

看起来像是popup使用transform居中，导致内部的fixed基于popup偏移了