更新前端静态网页获取方式，放弃使用后端获取api

frontend/node_modules/mdn-data/css/index.js

@@ -0,0 +1,8 @@
+module.exports = {
+  atRules:    require('./at-rules'),
+  selectors:  require('./selectors'),
+  types:      require('./types'),
+  properties: require('./properties'),
+  syntaxes:   require('./syntaxes'),
+  units:      require('./units'),
+}