fix(storybook): postcss parsing error for node_modules paths

Author: castastrophe

.storybook/postcss.config.js

@@ -5,10 +5,14 @@ const warnCleaner = require("postcss-warn-cleaner");
 const simpleBuilder = require("@spectrum-css/component-builder-simple/css/processors.js");
 const legacyBuilder = require("@spectrum-css/component-builder/css/processors.js");
 
+function getPackageFromPath(filePath) {
+	return filePath.match(`(components|@spectrum-css)\/(.*?)\/`)?.[2];
+}
+
 module.exports = (ctx) => {
 	let plugins = [];
 	const componentPath = resolve(__dirname, "../components");
-	const folderName = ctx.file.includes('node_modules') ? relative(resolve(__dirname, "../../node_modules/@spectrum-css"), ctx.file)?.split(sep)?.shift() : relative(componentPath, ctx.file).split("/")[0];
+	const folderName = getPackageFromPath(ctx.file) ?? "tokens";
 	const pkgPath = resolve(componentPath, folderName, "package.json");
 
 	if (["expressvars", "vars", "tokens"].includes(folderName)) {