fix: styles.css is not declared in package.json (#508)

Author: molvqingtai

package.json

@@ -3,9 +3,12 @@
   "version": "1.7.0",
   "description": "An opinionated toast component for React.",
   "exports": {
-    "types": "./dist/index.d.ts",
-    "import": "./dist/index.mjs",
-    "require": "./dist/index.js"
+    ".": {
+      "types": "./dist/index.d.ts",
+      "import": "./dist/index.mjs",
+      "require": "./dist/index.js"
+    },
+    "./dist/styles.css": "./dist/styles.css"
   },
   "main": "./dist/index.js",
   "types": "./dist/index.d.ts",