Create workflow for theme

.github/workflows/optimize-css.yml

@@ -0,0 +1,28 @@
+name: Optimize CSS
+
+on:
+  push:
+    paths:
+      - public/theme/source.css
+
+jobs:
+  optimize-css:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Install CSSO and CSSO-cli
+        run: npm install -g csso csso-cli
+
+      - name: Optimize CSS
+        run: csso public/theme/source.css --output public/theme/fixedsource.css
+
+      - name: Commit and push changes
+        run: |
+          git config --global user.name 'github-actions[bot]'
+          git config --global user.email 'github-actions[bot]@users.noreply.github.com'
+          git add public/theme/fixedsource.css
+          git commit -m 'Optimize theme CSS'
+          git push