If you use webpack with SCSS or LESS, you need extract CSS select string with ID that webpack added. For the sake of the example: I have selector:
#contacts-wrapper .animated-btn:before
So, webpack compile it with particular ID in something like:
#contacts-wrapper .animated-btn[_v-5061616a]:before
You can see it in dev tools. Therefore you need write in code this way:
CSSRulePlugin.getRule('#contacts-wrapper .animated-btn[_v-5061616a]:before')