fix(web-demo): add css loader for react-json-view-lite

react-json-view-lite imports a plain .css file which webpack
could not process as only .scss was handled. Add css-loader
rules to both dev and prod webpack configs.

TICKET: VL-5111

Author: roshan-bitgo

modules/web-demo/webpack/base.config.js

@@ -96,6 +96,10 @@ const rules = [
 
 const devRules = [
   ...rules,
+  {
+    test: /\.css$/,
+    use: ['style-loader', 'css-loader'],
+  },
   {
     test: /\.scss$/,
     use: [
@@ -118,6 +122,10 @@ const devRules = [
 
 const prodRules = [
   ...rules,
+  {
+    test: /\.css$/,
+    use: [MiniCssExtractPlugin.loader, 'css-loader'],
+  },
   {
     test: /\.scss$/,
     use: [