用vue-cli生成的项目，再其APP.VUE中引入bootstrap import './assets/css/bootstrap.css报错，如下

This relative module was not found:

* ./assets/css/bootstrap.css in ./~/.6.4.1@babel-loader/lib!./~/.11.1.4@vue-loader/lib/selector.js?type=script&index=0!./src/App.vue
> Listening at http://localhost:8080

webpack.base.conf.js中这么写

module: {
    rules: [
      {
        test: /\.(js|vue)$/,
        loader: 'eslint-loader',
        enforce: "pre",
        include: [resolve('src'), resolve('test')],
        options: {
          formatter: require('eslint-friendly-formatter')
        }
      },
      {
        test: /\.vue$/,
        loader: 'vue-loader',
        options: vueLoaderConfig
      },
      {
        test: /\.js$/,
        loader: 'babel-loader',
        include: [resolve('src'), resolve('test')]
      },
      {
        test: /\.css$/, 
        loader: 'style-loader!css-loader',
         options: vueLoaderConfig
      },
      {
        test: /\.(png|jpe?g|gif|svg)(\?.*)?$/,
        loader: 'url-loader',
        query: {
          limit: 10000,
          name: utils.assetsPath('img/[name].[hash:7].[ext]')
        }
      },
      {
        test: /\.(woff2?|eot|ttf|otf)(\?.*)?$/,
        loader: 'url-loader',
        query: {
          limit: 10000,
          name: utils.assetsPath('fonts/[name].[hash:7].[ext]')
        }
      }
    ]

请教下大神这什么情况啊，搞半天了