npm添加less less-loader sass-resources-loader
修改nuxt.config.js

build: {
    extend(config, ctx) {
      const sassResourcesLoader = {
        loader: 'sass-resources-loader',
        options: {
          resources: ['assets/style/theme.less', 'assets/style/mixins.less']
        }
      }
      config.module.rules.forEach(rule => {
        if (rule.test.toString() === '/\\.vue$/') {
          rule.options.loaders.less.push(sassResourcesLoader)
        }
        if (rule.test.toString() === '/\\.less$/') {
          rule.use.push(sassResourcesLoader)
        }
      })
    }
  }