If main.css exists, pass path down to bootstrap plugin

Author: KaneFreeman

src/base.config.ts

@@ -498,6 +498,7 @@ export default function webpackConfigFactory(args: any): webpack.Configuration {
 			args.locale && new CldrPlugin(),
 			new webpack.DefinePlugin({
 				__MAIN_ENTRY: JSON.stringify(mainEntryPath),
+				__MAIN_CSS_PATH: JSON.stringify(existsSync(mainCssPath) ? mainCssPath : null),
 				__DOJO_SCOPE: `'${libraryName}'`
 			}),
 			!isExperimentalSpeed &&
@@ -515,6 +516,7 @@ export default function webpackConfigFactory(args: any): webpack.Configuration {
 			!singleBundle &&
 				new BootstrapPlugin({
 					entryPath: mainEntryPath,
+					cssPath: existsSync(mainCssPath) ? mainCssPath : null,
 					shimModules: [
 						{
 							module: '@dojo/framework/shim/IntersectionObserver',