"vue-cli-service build" transform css calc()

Hi
I just created vue project using vue-cli

when I build, calc() css is transformed to result value.

my css:

<style>
 #app {
    width: calc(100% / 3);
  }
</style>

is transfromed to

#app {
  width: 33.33333%;
}

and dependencies are:

@vue/cli-plugin-babel@4.5.15
@vue/cli-service@4.5.15
core-js@3.19.1
vue@2.6.14
vue-template-compiler@2.6.14

probably it looks same, but I wanna prevserve it.

How to prevent vue-cli from changing calc?
Thanks.