feat(css): add Base UI theme demo

packages/css-base-ui/package.json

@@ -0,0 +1,25 @@
+{
+  "$schema": "https://json.schemastore.org/package.json",
+  "name": "@opencode-ai/css-base-ui",
+  "version": "1.18.4",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "dev": "vite --host 0.0.0.0",
+    "build": "vite build --base=./ && bun script/inline.ts",
+    "typecheck": "tsgo --noEmit"
+  },
+  "dependencies": {
+    "@base-ui/react": "1.6.0",
+    "@opencode-ai/css": "workspace:*",
+    "react": "19.2.7",
+    "react-dom": "19.2.7"
+  },
+  "devDependencies": {
+    "@types/react": "19.2.17",
+    "@types/react-dom": "19.2.3",
+    "@typescript/native-preview": "catalog:",
+    "@vitejs/plugin-react": "6.0.3",
+    "vite": "8.1.4"
+  }
+}