diff --git a/packages/redux-devtools-ui/package.json b/packages/redux-devtools-ui/package.json
index a06c3e6c..46278bff 100644
--- a/packages/redux-devtools-ui/package.json
+++ b/packages/redux-devtools-ui/package.json
@@ -16,7 +16,7 @@
   "main": "lib/cjs/index.js",
   "module": "lib/esm/index.js",
   "types": "lib/types/index.d.ts",
-  "sideEffects": false,
+  "sideEffects": ["*.css"],
   "repository": {
     "type": "git",
     "url": "https://github.com/reduxjs/redux-devtools.git"