diff --git a/package.json b/package.json
index 357cbac..ae0e489 100644
--- a/package.json
+++ b/package.json
@@ -52,5 +52,9 @@
 		"@storybook/addon-docs": "^10.2.16",
 		"playwright": "^1.58.2",
 		"@vitest/browser-playwright": "^4.0.18"
+	},
+	"dependencies": {
+		"clsx": "^2.1.1",
+		"tailwind-merge": "^3.5.0"
 	}
 }
diff --git a/src/shared/lib/cn.test.ts b/src/shared/lib/cn.test.ts
new file mode 100644
index 0000000..30e1b43
--- /dev/null
+++ b/src/shared/lib/cn.test.ts
@@ -0,0 +1,16 @@
+import { describe, expect, it } from 'vitest';
+import { cn } from './cn';
+
+describe('cn', () => {
+    it('merges class strings', () => {
+        expect(cn('foo', 'bar')).toBe('foo bar');
+    });
+
+    it('deduplicates conflicting Tailwind classes (last wins)', () => {
+        expect(cn('p-4', 'p-8')).toBe('p-8');
+    });
+
+    it('ignores falsy values', () => {
+        expect(cn('foo', false, undefined, null, 'bar')).toBe('foo bar');
+    });
+});
diff --git a/src/shared/lib/cn.ts b/src/shared/lib/cn.ts
new file mode 100644
index 0000000..c18709b
--- /dev/null
+++ b/src/shared/lib/cn.ts
@@ -0,0 +1,7 @@
+import { clsx, type ClassValue } from 'clsx';
+import { twMerge } from 'tailwind-merge';
+
+/** Merge Tailwind classes without conflicts. Later classes win on collision. */
+export function cn(...inputs: ClassValue[]): string {
+    return twMerge(clsx(inputs));
+}
diff --git a/src/shared/lib/index.ts b/src/shared/lib/index.ts
index b1c13e7..71e048f 100644
--- a/src/shared/lib/index.ts
+++ b/src/shared/lib/index.ts
@@ -1 +1,2 @@
 export * from './api';
+export { cn } from './cn';
diff --git a/vitest.unit.config.ts b/vitest.unit.config.ts
new file mode 100644
index 0000000..f2217ce
--- /dev/null
+++ b/vitest.unit.config.ts
@@ -0,0 +1,34 @@
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+import { svelte } from "@sveltejs/vite-plugin-svelte";
+import { defineConfig } from "vitest/config";
+
+const dirname =
+	typeof __dirname !== "undefined"
+		? __dirname
+		: path.dirname(fileURLToPath(import.meta.url));
+
+export default defineConfig({
+	plugins: [
+		svelte({
+			hot: !process.env.VITEST,
+		}),
+	],
+	test: {
+		globals: true,
+		environment: "jsdom",
+		setupFiles: ["./src/tests/setup.ts"],
+		include: ["src/**/*.{test,spec}.{js,ts}"],
+		exclude: ["src/tests/e2e/**/*.{test,spec}.{js,ts}"],
+	},
+	resolve: {
+		alias: {
+			$lib: path.resolve("./src/lib"),
+			$shared: path.resolve("./src/shared"),
+			$pages: path.resolve("./src/pages"),
+			$features: path.resolve("./src/features"),
+			$entities: path.resolve("./src/entities"),
+			$widgets: path.resolve("./src/widgets"),
+		},
+	},
+});