title: Use / deep / bug in Vue
body: <p>I used SCSS in vue-lic3, but there was a strange bug, using / deep / will report errors, I don't want to see it.</p>
  
  <p>Code Running Environment
  vue-cli3 + vant + scss</p>
  
  <p>css</p>
  
  <pre><code>/deep/ .van-tabs__content.van-tabs__content--animated,
    .van-tabs--line,
    .van-pull-refresh,
    .van-pull-refresh__track {
      height: 100%;
    }
  </code></pre>
  
  <p>vue.config.js</p>
  
  <pre><code>css: {
      loaderOptions: {
        sass: {
          data: `@import "~@/style/module.scss";`
        }
      }
    },
  </code></pre>
  
  <p>error</p>
  
  <pre><code>Failed to compile with 1 errors                                                                                                                                                                           14:14:46
   error  in ./src/views/RankingList.vue?vue&amp;type=style&amp;index=0&amp;lang=scss&amp;
  
  Module build failed (from ./node_modules/sass-loader/lib/loader.js):
  
    .van-tabs--line,
   ^
        Expected selector.
      ╷
  274 │   /deep/ .van-tabs__content.van-tabs__content--animated,
      │   ^
      ╵
    stdin 274:3  root stylesheet
        in F:\web\project-a\src\views\RankingList.vue (line 274, column 3)
  
   @ ./node_modules/vue-style-loader??ref--8-oneOf-1-0!./node_modules/css-loader/dist/cjs.js??ref--8-oneOf-1-1!./node_modules/vue-loader/lib/loaders/stylePostLoader.js!./node_modules/postcss-loader/src??ref--8-oneOf-1-2!./node_modules/sass-loader/lib/loader.js??ref--8-oneOf-1-3!./node_modules/cache-loader/dist/cjs.js??ref--0-0!./node_modules/vue-loader/lib??vue-loader-options!./src/views/RankingList.vue?vue&amp;type=style&amp;index=0&amp;lang=scss&amp; 4:14-444 14:3-18:5 15:22-452
   @ ./src/views/RankingList.vue?vue&amp;type=style&amp;index=0&amp;lang=scss&amp;
   @ ./src/views/RankingList.vue
   @ ./src/router.js
   @ ./src/main.js
   @ multi (webpack)-dev-server/client?http://192.168.100.15:8080/sockjs-node (webpack)/hot/dev-server.js ./src/main.js
  </code></pre>