diff --git a/biome.json b/biome.json
index d8acdbc76..a13791a44 100644
--- a/biome.json
+++ b/biome.json
@@ -46,5 +46,13 @@
       "indentWidth": 2,
       "lineWidth": 80
     }
+  },
+  "css": {
+    "formatter": {
+      "enabled": true,
+      "indentStyle": "space",
+      "indentWidth": 2,
+      "lineWidth": 80
+    }
   }
 }
diff --git a/dev/outer.css b/dev/outer.css
index 7e0fbef19..46694b407 100644
--- a/dev/outer.css
+++ b/dev/outer.css
@@ -1,4 +1,4 @@
 /* Emulate an outer css file */
 p {
-	line-height:1.5em;
-}
\ No newline at end of file
+  line-height: 1.5em;
+}
diff --git a/package.json b/package.json
index 1c612b90e..e4a972069 100644
--- a/package.json
+++ b/package.json
@@ -74,6 +74,9 @@
     "*.json": [
       "npx @biomejs/biome format --write"
     ],
+    "*.css": [
+      "npx @biomejs/biome format --write"
+    ],
     "*.less": [
       "npx @biomejs/biome format --write"
     ],