code: function (prefix = '') {
    return postcss.plugin('addClassPrefix', () => root => {
      root.walk(child => {
        if (child.type === 'rule') {
          const selectors = []
  
          child.selectors.forEach(selector => {
            // 处理 class 选择器
            selectors.push(selector.replace(/\.([-_a-zA-Z0-9]+)/ig, (all, $1) => `.${prefix}--${$1}`))
          })
  
          child.selectors = selectors
        }
      })
    })
  }
docs: 追加 class 前缀插件