diff --git a/.github/workflows/check.yml b/.github/workflows/check.yml
index 3c184a9c6..a4c70d3ae 100644
--- a/.github/workflows/check.yml
+++ b/.github/workflows/check.yml
@@ -33,7 +33,7 @@ jobs:
         run: pnpm install
 
       - name: Check
-        run: pnpm check
+        run: pnpm check-ci
 
       - name: Test
         run: pnpm test
diff --git a/.vscode/settings.json b/.vscode/settings.json
index 5fd3f8597..2eca1080c 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -5,9 +5,6 @@
   },
   "editor.defaultFormatter": "biomejs.biome",
   "editor.formatOnSave": true,
-  "[css]": {
-    "editor.defaultFormatter": "esbenp.prettier-vscode"
-  },
   "[yaml]": {
     "editor.defaultFormatter": "esbenp.prettier-vscode"
   },
diff --git a/biome.json b/biome.json
index c16e51e92..6caedf3c9 100644
--- a/biome.json
+++ b/biome.json
@@ -14,10 +14,22 @@
   "linter": {
     "rules": {
       "correctness": {
-        "noUnusedImports": "warn",
-        "noUnusedVariables": "warn",
-        "useHookAtTopLevel": "warn"
+        "noUnusedImports": "error",
+        "noUnusedVariables": "error",
+        "useHookAtTopLevel": "error"
+      },
+      "nursery": {
+        "useImportExtensions": "error"
       }
     }
+  },
+  "css": {
+    "formatter": {
+      "enabled": true,
+      "indentStyle": "space"
+    },
+    "linter": {
+      "enabled": true
+    }
   }
 }
diff --git a/lefthook.yml b/lefthook.yml
index 8024bebd8..cdf634c03 100644
--- a/lefthook.yml
+++ b/lefthook.yml
@@ -2,10 +2,10 @@ pre-commit:
   parallel: true
   commands:
     biome:
-      glob: "*.{js,cjs,mjs,ts,cts,mts,jsx,tsx,json,jsonc}"
-      run: pnpm biome check --apply --no-errors-on-unmatched {staged_files}
+      glob: "*.{js,cjs,mjs,ts,cts,mts,jsx,tsx,json,jsonc,css}"
+      run: pnpm biome check --write --no-errors-on-unmatched {staged_files}
       stage_fixed: true
     prettier:
-      glob: "*.{css,yml,yaml,md,markdown}"
+      glob: "*.{yml,yaml,md,markdown}"
       run: pnpm prettier --write {staged_files}
       stage_fixed: true
diff --git a/package.json b/package.json
index 9cc5285da..631ee2efc 100644
--- a/package.json
+++ b/package.json
@@ -57,11 +57,15 @@
   "scripts": {
     "build": "tsx scripts/build.ts",
     "check": "pnpm run /^check:/",
-    "check:biome": "biome check .",
+    "check:biome": "biome check",
     "check:prettier": "prettier --check .",
     "check:tsc": "tsc",
+    "check-ci": "pnpm run /^check-ci:/",
+    "check-ci:biome": "biome ci --reporter=github",
+    "check-ci:prettier": "prettier --check .",
+    "check-ci:tsc": "tsc",
     "fix": "pnpm run /^fix:/",
-    "fix:biome": "biome check --apply .",
+    "fix:biome": "biome check --write",
     "fix:prettier": "prettier --write .",
     "generate-ruleset-parser": "lezer-generator src/scripts/ruleset/ruleset.grammar -o src/scripts/ruleset/parser.js --noTerms",
     "generate-third-party-notices": "tsx scripts/generate-third-party-notices.ts",
diff --git a/src/scripts/options/from-now.tsx b/src/scripts/options/from-now.tsx
index c6b50e04b..b82218caa 100644
--- a/src/scripts/options/from-now.tsx
+++ b/src/scripts/options/from-now.tsx
@@ -1,7 +1,7 @@
 import dayjs from "dayjs";
 import dayjsRelativeTime from "dayjs/plugin/relativeTime";
 import { useEffect, useState } from "react";
-import "../dayjs-locales";
+import "../dayjs-locales.ts";
 import { translate } from "../locales.ts";
 
 dayjs.extend(dayjsRelativeTime);
diff --git a/src/scripts/options/set-interval-item.tsx b/src/scripts/options/set-interval-item.tsx
index 0a5941f79..cc94887e9 100644
--- a/src/scripts/options/set-interval-item.tsx
+++ b/src/scripts/options/set-interval-item.tsx
@@ -3,7 +3,7 @@ import { useState } from "react";
 import { ControlLabel, LabelWrapper } from "../components/label.tsx";
 import { Row, RowItem } from "../components/row.tsx";
 import { useClassName } from "../components/utilities.ts";
-import "../dayjs-locales";
+import "../dayjs-locales.ts";
 import { saveToLocalStorage } from "../local-storage.ts";
 import { translate } from "../locales.ts";
 import { useOptionsContext } from "./options-context.tsx";
diff --git a/src/scripts/options/sync-section.tsx b/src/scripts/options/sync-section.tsx
index 1d1092282..fb09d549b 100644
--- a/src/scripts/options/sync-section.tsx
+++ b/src/scripts/options/sync-section.tsx
@@ -33,7 +33,7 @@ import {
 import { Text } from "../components/text.tsx";
 import { TextArea } from "../components/textarea.tsx";
 import { usePrevious } from "../components/utilities.ts";
-import "../dayjs-locales";
+import "../dayjs-locales.ts";
 import { getWebsiteURL, translate } from "../locales.ts";
 import { addMessageListeners, sendMessage } from "../messages.ts";
 import { supportedClouds } from "../supported-clouds.ts";