fix: playground scaffolding include antd styles via index.css

Author: keydunov

packages/cubejs-playground/src/DashboardSource.js

@@ -12,6 +12,7 @@ import DashboardStoreSnippet from "./source/DashboardStoreSnippet";
 import SourceSnippet from "./source/SourceSnippet";
 
 const indexCss = `
+@import '~antd/dist/antd.css';
 body {
   background-color: #f0f2f5 !important;
 }
@@ -64,7 +65,7 @@ class DashboardSource {
 
   async persist() {
     const updateIndexCss = this.appLayoutAdded ? [
-      { ...this.indexCssFile, content: this.indexCssFile.content + indexCss }
+      { ...this.indexCssFile, content: indexCss }
     ] : [];
     const toPersist = this.filesToPersist.concat(
       Object.keys(this.fileToTargetSource).map(fileName => ({

packages/cubejs-playground/src/scaffolding/react/App.js

@@ -1,7 +1,5 @@
 import React from "react";
 import { ApolloProvider } from '@apollo/react-hooks';
-import "antd/dist/antd.css";
-import "./index.css";
 import { Layout } from "antd";
 import client from "./graphql/client";
 import Header from "./components/Header";