Prepend main css file to the main bundle's css file

(cherry picked from commit 3a0c0fb)

Author: KaneFreeman

.gitignore

@@ -6,3 +6,4 @@ npm-debug.log
 yarn.lock
 /test-app/package-lock.json
 /test-app/.dojorc
+.vscode/

src/base.config.ts

@@ -245,7 +245,6 @@ export default function webpackConfigFactory(args: any): webpack.Configuration {
 		staticOnly.push('build-elide');
 		entry = {
 			[bootstrapEntry]: removeEmpty([
-				existsSync(mainCssPath) ? mainCssPath : null,
 				'@dojo/framework/shim/Promise',
 				'@dojo/webpack-contrib/bootstrap-plugin/async'
 			])
@@ -500,6 +499,14 @@ export default function webpackConfigFactory(args: any): webpack.Configuration {
 				__MAIN_ENTRY: JSON.stringify(mainEntryPath),
 				__DOJO_SCOPE: `'${libraryName}'`
 			}),
+			!singleBundle &&
+				existsSync(mainCssPath) &&
+				new WrapperPlugin({
+					test: new RegExp(`${mainEntry}.*(\.css$)`),
+					header: () => {
+						return readFileSync(mainCssPath);
+					}
+				}),
 			!isExperimentalSpeed &&
 				new OptimizeCssAssetsPlugin({
 					cssProcessor: cssnano,