diff --git a/packages/core/package.json b/packages/core/package.json
index 84181ab..49f3744 100644
--- a/packages/core/package.json
+++ b/packages/core/package.json
@@ -21,6 +21,7 @@
     "typescript"
   ],
   "type": "module",
+  "sideEffects": false,
   "main": "./dist/index.cjs",
   "module": "./dist/index.js",
   "types": "./dist/index.d.ts",
diff --git a/packages/create-markdown/package.json b/packages/create-markdown/package.json
index de92a53..caf545a 100644
--- a/packages/create-markdown/package.json
+++ b/packages/create-markdown/package.json
@@ -25,6 +25,7 @@
     "typescript"
   ],
   "type": "module",
+  "sideEffects": false,
   "main": "./dist/index.cjs",
   "module": "./dist/index.js",
   "types": "./dist/index.d.ts",
diff --git a/packages/mdx/package.json b/packages/mdx/package.json
index bf6d17a..e9ed226 100644
--- a/packages/mdx/package.json
+++ b/packages/mdx/package.json
@@ -22,6 +22,7 @@
     "react"
   ],
   "type": "module",
+  "sideEffects": false,
   "main": "./dist/index.cjs",
   "module": "./dist/index.js",
   "types": "./dist/index.d.ts",
diff --git a/packages/preview/package.json b/packages/preview/package.json
index 93683c6..b935f5c 100644
--- a/packages/preview/package.json
+++ b/packages/preview/package.json
@@ -23,6 +23,7 @@
     "typescript"
   ],
   "type": "module",
+  "sideEffects": ["**/*.css"],
   "main": "./dist/index.cjs",
   "module": "./dist/index.js",
   "types": "./dist/index.d.ts",
diff --git a/packages/react/package.json b/packages/react/package.json
index f0ac4a6..c829891 100644
--- a/packages/react/package.json
+++ b/packages/react/package.json
@@ -21,6 +21,7 @@
     "typescript"
   ],
   "type": "module",
+  "sideEffects": false,
   "main": "./dist/index.cjs",
   "module": "./dist/index.js",
   "types": "./dist/index.d.ts",