diff --git a/package.json b/package.json
index d7d7819..9a80a50 100644
--- a/package.json
+++ b/package.json
@@ -28,7 +28,7 @@
     "markdown-it-anchor": "^5.2.5"
   },
   "dependencies": {
-    "clean-css": "^4.2.1",
+    "clean-css": "^5.1.4",
     "html-minifier": "^4.0.0",
     "uglify-es": "^3.3.9"
   }
diff --git a/yarn.lock b/yarn.lock
index 2356204..4080785 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -583,6 +583,12 @@ clean-css@^4.1.11, clean-css@^4.2.1:
   dependencies:
     source-map "~0.6.0"
 
+clean-css@^5.1.4:
+  version "5.1.4"
+  resolved "https://registry.yarnpkg.com/clean-css/-/clean-css-5.1.4.tgz#d191c98347f9fc36b301f99bb827898151175782"
+  dependencies:
+    source-map "~0.6.0"
+
 cliui@^2.1.0:
   version "2.1.0"
   resolved "https://registry.yarnpkg.com/cliui/-/cliui-2.1.0.tgz#4b475760ff80264c762c3a1719032e91c7fea0d1"