Fix Tailwind CSS v4→v3 downgrade

package.json

@@ -19,7 +19,6 @@
     "react-dom": "^19.2.5"
   },
   "devDependencies": {
-    "@tailwindcss/postcss": "^4.2.2",
     "@types/react": "^19.2.14",
     "@types/react-dom": "^19.2.3",
     "@vitejs/plugin-react": "^6.0.1",
@@ -29,7 +28,7 @@
     "lucide-react": "^1.8.0",
     "mammoth": "^1.12.0",
     "postcss": "^8.5.10",
-    "tailwindcss": "^4.2.2",
+    "tailwindcss": "^3.4.19",
     "tesseract.js": "^7.0.0",
     "typescript": "^6.0.3",
     "vite": "^8.0.8"