add lost ngprogress css

src/main.js

 import ElementUI from 'element-ui'
 import 'element-ui/lib/theme-default/index.css'
 import NProgress from 'nprogress'
+import 'nprogress/nprogress.css'
 import 'normalize.css/normalize.css'
 import '@/assets/iconfont/iconfont'
 import IconSvg from '@/components/Icon-svg/index.vue'