change theme to themeset

.gitea/workflows/build.yaml

@@ -27,7 +27,7 @@ jobs:
       - name: build presentation
         working-directory: ./presentation
         run: |
-          npx @marp-team/marp-cli@latest --theme themes/cantor.css presentation.md -o index.html && \
+          npx @marp-team/marp-cli@latest --theme-set ./themes presentation.md -o index.html && \
           zip -r ../presentation.zip .
       - name: upload to pages
         run: |