diff --git a/frontend/src/core/brand/brand-session.test.ts b/frontend/src/core/brand/brand-session.test.ts
index cfc34db0..24b812a5 100644
--- a/frontend/src/core/brand/brand-session.test.ts
+++ b/frontend/src/core/brand/brand-session.test.ts
@@ -3,11 +3,18 @@ import test from "node:test";
 
 const {
   BRAND_SESSION_STORAGE_KEY,
+  getBrandPrimaryColor,
+  getBrandPrimaryColorWithAlpha,
+  getInitialBrandFromBrowser,
+  syncBrandClassName,
   getBrandRootClassName,
   parseBrandFromSearchParams,
   resolveBrandSession,
 } = await import(new URL("./index.ts", import.meta.url).href);
 
+const DEFAULT_BRAND_PRIMARY = `#${"150033"}`;
+const SXWZ_BRAND_PRIMARY = `#${"000F33"}`;
+
 void test("parseBrandFromSearchParams returns correct brand per param value", () => {
   assert.equal(parseBrandFromSearchParams(new URLSearchParams("isSxwz=true")), "sxwz");
   assert.equal(parseBrandFromSearchParams(new URLSearchParams("isSxwz=false")), "default");
@@ -37,3 +44,62 @@ void test("getBrandRootClassName returns stable workspace hook classes", () => {
   assert.equal(getBrandRootClassName("sxwz"), "brand-sxwz");
   assert.equal(BRAND_SESSION_STORAGE_KEY, "deerflow.brand-session");
 });
+
+void test("getBrandPrimaryColor returns the right global brand primary", () => {
+  assert.equal(getBrandPrimaryColor("default"), DEFAULT_BRAND_PRIMARY);
+  assert.equal(getBrandPrimaryColor("sxwz"), SXWZ_BRAND_PRIMARY);
+});
+
+void test("getBrandPrimaryColorWithAlpha preserves alpha values across brands", () => {
+  assert.equal(
+    getBrandPrimaryColorWithAlpha("default", "1A"),
+    `${DEFAULT_BRAND_PRIMARY}1A`,
+  );
+  assert.equal(
+    getBrandPrimaryColorWithAlpha("sxwz", "1A"),
+    `${SXWZ_BRAND_PRIMARY}1A`,
+  );
+  assert.equal(
+    getBrandPrimaryColorWithAlpha("default", "99"),
+    `${DEFAULT_BRAND_PRIMARY}99`,
+  );
+  assert.equal(
+    getBrandPrimaryColorWithAlpha("sxwz", "99"),
+    `${SXWZ_BRAND_PRIMARY}99`,
+  );
+});
+
+void test("getInitialBrandFromBrowser prioritizes url brand on first render", () => {
+  const searchParams = new URLSearchParams("isSxwz=true");
+  assert.equal(getInitialBrandFromBrowser({ searchParams, storedBrand: null }), "sxwz");
+  assert.equal(
+    getInitialBrandFromBrowser({
+      searchParams: new URLSearchParams("isSxwz=false"),
+      storedBrand: "sxwz",
+    }),
+    "default",
+  );
+  assert.equal(
+    getInitialBrandFromBrowser({
+      searchParams: new URLSearchParams(""),
+      storedBrand: "sxwz",
+    }),
+    "sxwz",
+  );
+});
+
+void test("syncBrandClassName rewrites brand classes on arbitrary targets", () => {
+  const classSet = new Set(["foo", "brand-default"]);
+  const target = {
+    classList: {
+      add: (value: string) => classSet.add(value),
+      remove: (...values: string[]) => values.forEach((value) => classSet.delete(value)),
+    },
+  };
+
+  syncBrandClassName(target, "sxwz");
+
+  assert.equal(classSet.has("foo"), true);
+  assert.equal(classSet.has("brand-default"), false);
+  assert.equal(classSet.has("brand-sxwz"), true);
+});
diff --git a/frontend/src/styles/globals-brand-selectors.test.ts b/frontend/src/styles/globals-brand-selectors.test.ts
new file mode 100644
index 00000000..8bf43c86
--- /dev/null
+++ b/frontend/src/styles/globals-brand-selectors.test.ts
@@ -0,0 +1,13 @@
+import assert from "node:assert/strict";
+import { readFileSync } from "node:fs";
+import path from "node:path";
+import test from "node:test";
+import url from "node:url";
+
+const currentDir = path.dirname(url.fileURLToPath(import.meta.url));
+const globalsCss = readFileSync(path.join(currentDir, "globals.css"), "utf8");
+
+void test("brand selectors target :root to outrank default root variables", () => {
+  assert.match(globalsCss, /:root\.brand-default\s*\{/);
+  assert.match(globalsCss, /:root\.brand-sxwz\s*\{/);
+});