Vue build as web component with new JS features

hey, I am trying to build my Vue project as Web component, as you can see here
build target
but I can not do it because I am facing Issues with new JavaScript features
nullish coalescing, is erroring and the second inside question is about 3red party library which I use how can I add theme inside the app if I a Using app.vue as entry file

hey, I solved it
the answer in github