will squash before merge:

projects/npm-tools/packages/npm-scripts/src/utils/webpackScssLoader.js

@@ -15,7 +15,10 @@ module.exports = function (_content, _map, _meta) {
 
 	const webContextPath = getBndWebContextPath(projectDir);
 
-	let urlPath = path.relative(buildConfig.input, resourcePath);
+	let urlPath = path.posix.relative(
+		buildConfig.input,
+		resourcePath.split(path.sep).join(path.posix.sep)
+	);
 
 	urlPath = urlPath.replace(/scss$/, 'css');
 

projects/npm-tools/packages/npm-scripts/test/utils/webpackScssLoader.js

@@ -0,0 +1,39 @@
+/**
+ * SPDX-FileCopyrightText: © 2019 Liferay, Inc. <https://liferay.com>
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+const os = require('os');
+
+describe.only('windows test', () => {
+	it('returns relative path', () => {
+		const basePath = 'src/main/resources/META-INF/resources';
+
+		const resourcePath = path.join(
+			os.tmpdir(),
+			'src',
+			'main',
+			'resources',
+			'META-INF',
+			'resources',
+			'js',
+			'pages',
+			'RuleList.scss'
+		);
+
+		console.log('RESOURCE: ', resourcePath);
+
+		let oldPath = path.relative(basePath, resourcePath);
+
+		console.log('OLD: ', oldPath);
+
+		let newPath = path.posix.relative(
+			basePath,
+			resourcePath.split(path.sep).join(path.posix.sep)
+		);
+
+		console.log('NEW: ', newPath);
+
+		expect(oldPath).toBe(newPath);
+	});
+});