node_modules/vue-loader/lib/style-compiler/plugins/trim.js

const postcss = require('postcss')
module.exports = postcss.plugin('trim', opts => css => {
  css.walk(({ type, raws }) => {
    if (type === 'rule' || type === 'atrule') {
      raws.before = raws.after = '\n'
    }
  })
})