chore: add github action for checking file format

.github/workflows/check-format.yml

@@ -0,0 +1,24 @@
+name: check css format
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  check-format:
+    runs-on: ubuntu-latest
+    steps:
+    - name: checkout repository
+      uses: actions/checkout@v2
+    - name: install node.js and npm
+      uses: actions/setup-node@v2
+      with:
+        node-version: '20'
+    - name: install prettier
+      run: npm i prettier -g
+    - name: check format using prettier
+      run: prettier --check '*.css'